pmacs/docs/vterm-framing.md

Vterm — framing (Arc 5 stage 2, three-PR delivery)

Revision 9 — 2026-07-22. Status: Stage 1 landed on main as PR #126 at merge 643d1e1; Stage 2 landed as PR #130 at merge 86fc1bc; Stage 3 is IMPLEMENTED on vterm-gpu and awaits review. Revision 8's framing text below is preserved verbatim as the approved contract; §0.9 records what the implementation actually did, including the two places it had to go beyond the letter of the framing.

Revision 8 re-scouts the final stage against the integrated protocol-v18 tree and closes its remaining producer/frontend boundary decisions. Protocol v19 uses one validated complete TerminalFrame; a shared 8 MiB aggregate glyph budget keeps the largest legal postcard message below the existing 16 MiB transport cap instead of broadening every connection's allocation ceiling. The first-frame bootstrap is explicit: after every BufferSnapshot, a v19 GPU sends the document viewport and, when the drawable terminal cell size is nonzero, terminal-cell geometry; the daemon accepts only the declaration appropriate to the authenticated active buffer. Semantic terminal rendering is per frontend/window. Passive views never resize the PTY, and terminal mode retains existing statusline, menu, minibuffer, and BEL/clipboard channels while suppressing document projection and presence.

Revision 7's geometric at_bottom, fixed C-c transport escape, authenticated context-implicit Lua operations, durable controller and per-view identities, logical-cell anchors, frontend-explicit grid rendering, per-frontend dispatch, authenticated v18 input, local clipboard/BEL drainage, default-name uniquification, mouse override, and resize ordering remain unchanged. Main-screen resize reflows while alternate screen clips/pads; exited buffers remain with an Emacs-style process message; shared Style stays unchanged; and one BufferId owns one shared process/screen whose most recently accepted frontend/window context controls size.

This framing follows the compile-mode terminal substrate that landed in PR #113. src/process.rs already owns PTY creation, process groups, bounded readers, stdin writes, resize, exit/restart state, and final drain. src/ansi.rs already owns a streaming UTF-8/CSI/OSC parser, but deliberately emits only the line-oriented subset compile-mode needs. Vterm does not replace either subsystem. It extends their contracts and adds the missing terminal screen state machine.

Arc 5 stage 2 (vterm) ships as three separately reviewed internal stages, one PR each:

1. terminal core — full-screen VT events, TerminalScreen, internal session ownership/contracts, and headless real-PTY acceptance;
2. TUI integration — terminal-window composition, input, resize, scrollback, selection, and copy;
3. GPU integration — protocol v19 terminal messages, semantic-daemon routing, and a native GPU terminal renderer.

There is no single mega-PR. Each stage is useful and testable by itself, and a later stage starts only after the preceding stage lands on main.

0. Revision 8 — landed internal Stages 1–2 and framed Stage 3

The first of the three vterm PRs landed on main at merge 643d1e1. Implementation commits bbc1f33 and 962944b, first-review fixes through bf972a7, and second-review hardening through 9797ada shipped in PR #126, https://github.com/levineuwirth/pmacs/pull/126. That landed stage is deliberately headless; this Stage 2 branch adds the Lua and TUI surfaces while leaving GPU/protocol integration for Stage 3.

0.1 Public seam and ownership

src/terminal/session.rs exports:

• owned TerminalSpec { command, args, cwd, env, name, rows, cols, scrollback_rows }, with new and strict pre-side-effect validate;
• TerminalProcessState::{Running, Exited(i32), Signaled(String), Crashed(String)};
• owned TerminalSnapshot { buffer_id, size, cells, cursor, title, screen_generation, selection, scroll_offset, at_bottom, pid, process };
• SharedTerminalManager = Rc<RefCell<TerminalManager>>;
• TerminalManager::{new, len, is_empty, open, is_terminal, process_id, snapshot, tick, send, resize, terminate, prune, shutdown}.

The Stage 1 snapshot(BufferId) is intentionally context-free: selection=[], scroll_offset=0, and at_bottom=true. Stage 2 adds per-(FrontendId, WindowId, BufferId) state and an owned snapshot_for_view(...); it must not add a second screen.

EditorState owns the one shared manager. Tick order is supervisor tick → terminal-owned PID drain/watchdog/prune → process.after-tick; LSP, MCP, and ordinary Lua process events retain their existing owners. ProcessSpec gained an AnsiParserProfile: ProcessSpec::new and Lua ansi=true stay LineOriented, while terminal sessions explicitly request FullScreen. Synchronous unpublished terminal spawn failure emits no orphan process event.

Terminal identity buffers are pathless, clean, empty, and buffer-read-only. The guard runs before direct edits, split Lua begin/skip-intercept edits, undo/redo, and local/remote CRDT content import. Attaching an immutable empty CRDT for semantic identity remains valid.

0.2 Stage 1 acceptance mapping

All fourteen Stage 1 criteria are implemented:

1. whole/split parser equivalence: screen::tests::parser_split_points_produce_identical_screen plus the ANSI split matrix;
2. malformed/truncated/over-cap recovery: the 44 ansi::tests, including split UTF-8, ignored CSI/OSC/DCS, and forward-progress cases;
3. cursor/region/edit exactness: cursor_erase_insert_delete_scroll_and_margins_mutate_exact_regions;
4. pending wrap/wide/combining invariants: wide overwrite, split ZWJ/RI/ modifier/variation, right-edge, and continuation tests;
5. alternate/synchronized publication: alternate_screen_preserves_main_and_has_no_history, synchronized_output_gates_snapshot_and_finish_releases, and watchdog;
6. DEC G0/G1 + SI/SO: acs_and_device_replies_are_exact;
7. SGR fidelity and ignored attributes: ANSI SGR/color/underline tests plus screen operation coverage;
8. resize semantics: soft-wrap reflow, wide-boundary/cursor/hard-break tests, alternate clipping, and atomic invalid resize;
9. dual history limits: history_obeys_row_and_cell_caps;
10. bounded DA/DSR/CPR and unsupported-output safety: acs_and_device_replies_are_exact plus parser ignore cases;
11. strict owned specifications: strict_owned_spec_rejects_before_spawn_and_is_mutation_independent;
12. real adversarial PTY/final drain: final_output_precedes_exact_nonzero_annotation_and_buffer_is_retained splits ESC/CSI writes, observes addressed alternate-screen output while running, unblocks raw stdin through send, restores the main screen, and proves final output precedes the exact PID/outcome annotation; zero, non-zero, signal, wrapped, and one-row annotations are separately pinned;
13. lifecycle cleanup: transactional failure, live buffer-kill prune/reap, and TERM-ignoring editor shutdown acceptance;
14. read-only/CRDT invariants: default + CRDT shared acceptance and focused buffer unit tests cover every mutation route and empty bootstrap.

0.3 Final gates and bite

The initial delivery gate run fixed missing acceptance-crate documentation; PR CI then exposed Darwin's numeric strsignal suffix, fixed in 962944b. Review round 1's first Clippy pass found only identical LF/IND match arms, consolidated in bf972a7. Review round 2 added one screen unit and one shared acceptance case; the complete sequence restarted from gate 1:

• cargo fmt --check: clean;
• cargo clippy --workspace --all-targets -- -D warnings: clean;
• default library: 1,661 passed, 3 ignored;
• CRDT library: 1,837 passed, 3 ignored;
• Stage 1 acceptance: 9 default + 10 CRDT passed;
• M4 acceptance: 114 passed, 3 ignored, 1 basedpyright filtered;
• required GPU: 109 passed;
• workspace: 2,769 passed across 79 suites, 19 ignored, 1 filtered;
• git diff --check: clean.

scripts/bite main src/lib.rs --test vterm_stage1_acceptance returned bite: OK: the swapped pre-stage crate root cannot compile the new terminal API. This is explicitly the helper's weaker compile-time API bite, not a clean behavioral assertion failure.

scripts/bite HEAD^ src/ansi.rs --lib parser_split_points_produce_identical_screen returned bite: OK with a clean behavioral assertion failure: the pre-dispatch parser left the cursor at row zero/column four instead of applying NEL/RI/IND and landing at row one/column zero.

scripts/bite HEAD^ src/terminal/screen.rs --test vterm_stage1_acceptance terminal_cells_reject_child_control_characters returned bite: OK with a clean behavioral failure: the pre-hardening screen stored control bytes in a grapheme cluster rather than preserving the blank snapshot.

0.4 Stage 2 re-scout resolutions

The post-Stage 1 review and a fresh read of landed main found six load-bearing Stage 2 seams. This revision resolves them before code:

• PTY resize ownership is stored durably per terminal session as an authenticated (FrontendId, WindowId) controller. Render-time EditorCore::active_frontend is not an ownership signal.
• The single global KeyDispatcher cannot safely carry a terminal C-c continuation in a multi-frontend daemon. Pending dispatch and terminal escape state become per-FrontendId; dispatch-idle publication becomes frontend-specific too.
• Terminal copy reuses the existing kill-ring/clipboard setter. The in-process run loop must drain that signal and feed it through Frontend::present_messages; the TUI must implement InstanceSignal::Bell rather than drop it.
• RenderState::render_frame and paint_frame need the target FrontendId explicitly. A transient mutable active frontend may still attribute commands, but it may not select another frontend's layout, terminal view state, statusline context, or resize owner during fan-out.
• Current v18 daemon key/mouse payload IDs are client supplied. Stage 2 routes key, mouse, paste, focus, and resize through the authenticated connection source before any terminal ownership or PTY effect.
• The Stage 1 screen already preserves logical-line IDs and row cell offsets through main-screen reflow. Stage 2 selection and scroll anchors use those coordinates; numeric distance from the moving tail is derived metadata, never stored ownership state.

The final framing review pinned three precision contracts:

• at_bottom reports whether the live tail is currently visible; it is not the separate internal “follow future output” predicate.
• C-c is a consumed transport escape, not an ordinary dispatcher prefix map; C-c-leading user bindings are deliberately unavailable in terminal windows for Stage 2.
• Context-implicit Lua view operations require an authenticated interactive command origin and fail closed rather than borrowing a stale active_frontend.

Stage 3 additionally owns pmacs-gpu/src/attach.rs for gated terminal resize/pointer sending and coalescing. New daemon event variants apply the same authenticated-source rule. Wire-facing terminal state, selection, and limits live in or are re-exported from pmacs-protocol. Revision 8 resolves the complete-frame size finding with a shared 8 MiB aggregate glyph-byte bound: the maximum legal encoded frame is measured below the unchanged 16 MiB transport cap. The producer rejects rather than truncates or silently chunks an over-bound internal snapshot.

0.5 Stage 1 review round 1

The first external review found no ownership, mutation-guard, parser-cap, or security regressions. This round resolves its three merge-adjacent findings:

• ESC D (IND), ESC E (NEL), and ESC M (RI) are typed full-screen operations. RI scrolls down only at the top margin; IND/NEL scroll up at the bottom margin, with NEL additionally returning to column zero. The parser's every-byte-split matrix and focused screen-margin test pin the complete path.
• Terminal children no longer inherit an arbitrary host TERM; absent a caller override, their process environment gets TERM=xterm-256color.
• The TERM-ignoring shutdown acceptance uses kill(pid, 0) through nix instead of Linux-only /proc, so macOS now exercises the assertion.
• Resize retains every surviving application tab stop and installs default stops only in newly added columns.

spawn_ansi_parser intentionally calls AnsiParser::finish() on channel disconnect for both profiles. For existing line-oriented compile/REPL consumers, EOF therefore delivers trailing partial text and required synthetic style/alternate-screen balancing that older code dropped. This is an intentional latent-bug fix and an observable compatibility contract.

The Stage 2 Lua open surface must uniquify colliding default buffer names (*terminal:sh*, *terminal:sh*<2>, and so on) before terminal creation becomes user-visible.

0.6 Stage 1 review round 2

The second external review found no ownership, lifecycle, mutation-guard, transactional-spawn, final-drain, parser-cap, or reflow defects and judged Stage 1 merge-ready. Its renderer-boundary hardening and cheap cleanups are resolved before Stage 2:

• TerminalScreen::write_text drops every char::is_control() value before grapheme segmentation, so parser-produced C1 and direct-event C0/C1 bytes cannot enter copyable or renderable cells. Unit and shared acceptance tests pin a byte-identical blank snapshot.
• SGR mouse release reports retain the released left/middle/right button code and use the lowercase m final.
• The dead line_feed mode parameter and contradictory wide-grapheme branch are removed; all logical-line ID allocation saturates consistently; and terminal prune clears stale round-trip input membership.

Out-of-range DECSTBM bottom clamping, CSI-intermediate clone removal, and a separately named configuration-time scrollback-row cap remain explicit deferrals in §11.

0.7 Stage 2 landing and Stage 3 re-scout

Stage 2 landed on main as PR #130 at merge 86fc1bc after two review rounds. Its integrated tree is the Stage 3 base: protocol v18, four terminal view-state acceptance cases in both default and CRDT builds, 109 required-GPU tests, and the authenticated daemon/TUI seams described in §§5 and 9. Stage 3 does not reopen the landed escape, controller, selection, copy, resize, or Lua contracts.

The current tree exposes five Stage 3 integration facts that are now locked:

• A semantic frontend learns a buffer switch from BufferSnapshot, but an empty terminal identity snapshot does not identify itself as terminal. Therefore the GPU sends both its ordinary byte viewport and a version-gated terminal-cell size after each snapshot; the daemon ignores the inapplicable declaration. No buffer-kind flag or pixel geometry is added.
• The existing TUI layout adapter subtracts modelines and handles splits from a whole terminal size. Reusing it for the GPU would subtract chrome twice. Stage 3 adds exact active-window semantic adapters whose CellSize already describes the terminal content rectangle.
• screen_generation does not cover selection, scroll, or process-state changes. Silence is therefore based on equality of the complete ordered wire payload, not on any one generation counter.
• The legal Stage 1 cell bounds can exceed the 16 MiB transport cap when every cell carries a maximal combining cluster. Rather than raising the allocation ceiling for all pre-handshake and established messages, v19 adds an 8 MiB aggregate glyph-byte limit and proves the largest legal encoded frame stays below MAX_FRAME_BYTES.
• The GPU's document shaper cannot define terminal column origins. Terminal mode uses fixed cell geometry: explicit row/column rectangles own background, underline, selection, cursor, clipping, and hit testing; text runs are positioned at cell origins and never determine later cell positions.

0.8 Stage 3 framing review round 1

The first external Stage 3 review verified the Revision 8 base, named seams, limits, Stage 1/2 compatibility, and continuity state and found no architectural defect. This round closes its three precision findings:

• The measured maximum payload fixture now maximizes legal Style bytes on every cell and distributes the exact glyph budget across legal clusters with lengths chosen to maximize serialized length-prefix overhead.
• GPU acceptance names terminal copy through InstanceSignal::Clipboard and the existing OS clipboard path; it does not imply that child OSC 52 is honored.
• Arc 5 stage 2 is the vterm delivery; capitalized Stages 1–3 are its three internal PR stages.

0.9 Stage 3 as built

Stage 3 is implemented on vterm-gpu, cut from canonical main @ 1dd47fc rather than stacked on the documentation branch, with the approved Revision 8 framing as its first commit. Criteria 28–37 are implemented.

Protocol. pmacs-protocol gained src/terminal.rs, which now owns the shared row/column/visible-cell/grapheme/metadata bounds (re-exported from crate::terminal::* so every Stage 1/2 caller keeps its path and no duplicate type exists), TerminalProcessState, TerminalSelectionSpan, TerminalFrame, and TerminalFrame::validate. unicode-width was promoted to a workspace dependency so the terminal screen and the wire validator measure glyph columns with one table. Discriminants: InstanceMessage::TerminalFrame is 26, FrontendEvent::TerminalResize 11, TerminalPointer 12 — each appended after its enum's final v18 variant, with placement pins on StatuslineSegments and MenuPointer guarding them. SUPPORTED_PROTOCOL_VERSIONS is [6..=19].

The measured maximum legal frame — 512x512, one maximal selection span per row, maximum title and process metadata, the maximal-encoding Style on every cell, and the exact 8 MiB aggregate glyph budget distributed to maximize serialized length-prefix overhead — encodes to 13,437,863 bytes, against the unchanged 16,777,216-byte transport cap. A one-byte-over aggregate is rejected before serialization.

Two decisions the implementation had to make.

1. The Viewport gate keys on the ACTIVE buffer, not the declared one. §6.2 says "a document buffer accepts only Viewport; an active terminal buffer accepts only TerminalResize", and the first implementation read that as a test on the buffer the message names. That is not sufficient: Viewport also ALIGNS the frontend's window to the buffer it names, so a stale document viewport still in flight when a command opened a terminal dragged the frontend straight back off it — the real-daemon acceptance showed the window oscillating and no frame ever arriving. The daemon now drops Viewport when the authenticated source's active window shows a terminal (and, defensively, when the declared buffer is itself a terminal). This is the framing's own wording taken literally; it is recorded here because the weaker reading looks correct and silently produces a terminal that never paints.
2. The producer clears terminal mode on every exit path. in_terminal_mode is used daemon-side to suppress CursorByte and the presence sweep. An early return from the terminal pass that left the flag set kept those suppressed after the frontend went back to a document. Every path out of the pass now clears it explicitly.

Renderer. pmacs-gpu/src/terminal.rs is a pure, cell-space paint planner: it resolves a validated frame into background/underline/selection/cursor runs and explicitly positioned text runs, taking the frontend's two default colors as parameters so every paint rule is unit-testable without a GPU. main.rs holds a two-state machine (Document / Terminal), builds one shaped buffer per text run so a wide or cluster glyph's advance can never choose the next column's origin, and swaps the document quad/squiggle/caret/minimap/gutter batches for terminal ones while leaving the status band and popup layers alone.

Criterion 37. The GPU is a separate binary that depends only on pmacs-protocol, so the single real path is driven as a process: pmacs-gpu --headless-probe <socket> <report> attaches through the REAL attach client (the reader sink was generalized so the winit path and the probe share one handshake, outbox, and writer), presses a real key that opens a real /bin/sh child, applies real TerminalFrames, composites real pixels through render_to_view, sends real input and a real geometry change, and writes named observations the acceptance asserts on. tests/vterm_stage3_acceptance.rs a37_… is that test; it is CRDT-gated because the daemon advertises crdt_replica / semantic_render only on CRDT builds.

Verification (from a clean tree). cargo fmt --check; strict workspace Clippy; 1,757 default + 1,933 CRDT library tests (3 ignored each); Stage 1 acceptance 9 default + 10 CRDT; Stage 2 acceptance 4 default + 4 CRDT; Stage 3 acceptance 4 default + 5 CRDT (the fifth is the CRDT-gated real-daemon path); statusline acceptance 7 default + 8 CRDT; M4 120 passed (3 ignored, 1 filtered); required GPU 127; one-invocation workspace sweep 2,919 passed across 83 suites (19 ignored); git diff --check clean. One unexplained single failure of the required-GPU suite occurred once mid-session and did not reproduce across eight subsequent runs including the full sweep; its identity was not captured.

0.10 Stage 3 review round 1

PR #135's first review found no correctness blocker, confirmed the required-GPU suite clean across four runs (twelve total with the author's), and raised two design questions plus three minor notes. All five are addressed.

• Presence while in terminal mode (finding 1) — fix kept, prediction not reproduced. The review predicted that skipping the presence sweep freezes last_broadcast at the abandoned document position, leaving peers painting a stale caret. It does not: the buffer-follow clears the terminal declaration when it ships the snapshot, so terminal_active is false on the tick a window first shows a terminal, and the declaration cannot arrive until a later tick (the frontend learns the buffer id FROM that snapshot). One truthful sweep always lands first. A real-daemon two-frontend test written to catch the freeze passes against the pre-fix tree — the bite is VACUOUS, and it is labelled a regression guard rather than fix evidence. The skip is removed anyway: it was load-bearing on tick ordering and bought nothing, and its removal makes "presence follows the frontend" structural.
• Hover claimed durable control (finding 2) — real, fixed, bite-verified. apply_terminal_gesture claimed the controller before dispatching, including for Move, which does nothing. A semantic frontend reports motion at pixel rate, so sweeping the mouse across a PASSIVE split's terminal took durable control and the next layout sync resized the shared PTY to that background view's geometry — exactly the theft the controller rule exists to prevent. Bare motion no longer claims; every deliberate gesture still does. scripts/bite HEAD src/editor.rs on hover_does_not_steal_terminal_control_from_the_active_frontend is a clean behavioral bite (assertion failure, not a compile error).
• Terminal motion is deduplicated by cell (finding 3). Sub-cell motion resolved to the same coordinate and still crossed the wire, where each event is a daemon-side gesture. State::terminal_motion_is_new now gates it, and press/release re-arm the memo so the first drag after a press still reports. Its unit test cannot bite — the seam did not exist pre-fix — and says so.
• Declarations record only once sent (finding 4). terminal_declaration_if_changed is now a pure query and note_terminal_declaration_sent records, so a failed write is retried instead of suppressed as already-declared. The existing a35 test caught the contract change and now pins both halves.
• Unchanged frames are no longer re-validated (finding 5). The complete payload comparison runs before validate; only validated frames are ever stored, so a frame equal to the baseline has already passed. The chrome tail is factored into terminal_chrome so both exits emit it identically.

Post-review gates: cargo fmt --check; strict workspace Clippy; 1,757 default + 1,933 CRDT library tests; Stage 1 acceptance 9/10, Stage 2 4/4, Stage 3 5/7, statusline 7/8 (default/CRDT); M4 120; required GPU 128; workspace sweep 2,921 across 83 suites (19 ignored); git diff --check clean.

1. Problem and ownership boundary

Pmacs can supervise a PTY and can parse enough ANSI to turn command output into a line-oriented compilation buffer. It cannot host nvim, htop, a shell using cursor motion, or any other application whose output means “mutate a terminal screen” rather than “append text.” The current parser intentionally recognizes and discards cursor addressing, alternate-screen state, scrolling, and most terminal modes. The editor renderer only knows an ordinary rope and its views.

The missing abstraction is a real terminal state machine:

PTY bytes -> AnsiParser -> terminal operations -> TerminalScreen
                                               -> response bytes -> PTY stdin
Frontend input -> terminal input encoder ------------------------^ 

TerminalScreen -> TUI cell composition
               -> protocol v19 TerminalFrame -> GPU cell layout

Ownership is explicit:

• ProcessSupervisor owns the child, PTY file descriptors, bounded worker pipeline, signal delivery, and final drain.
• AnsiParser owns byte-stream framing and escape-sequence decoding. It does not own a screen.
• TerminalScreen owns main/alternate grids, cursor and modes, scroll regions, tab stops, and scrollback.
• TerminalManager owns the mapping from a special editor BufferId to one PTY process plus one TerminalScreen, and owns per-window/per-frontend scroll/selection state.
• The ordinary buffer is an identity and lifecycle anchor only. Terminal screen contents are never mirrored into its rope.
• TUI and GPU frontends own final glyph drawing. They consume cells; they do not reinterpret ANSI or maintain a second VT state machine.

This keeps the existing semantics-down boundary intact. Document text remains a CRDT/rope semantic surface. A terminal is inherently a cell protocol, so its new wire family carries terminal cells, not daemon-formatted document text and not pixels.

2. Ground truth in the current tree

The implementation must preserve these existing contracts:

• ProcessMode::Pty, write_stdin, resize_pty, group-directed signals, bounded output channels, and the TERM/KILL final drain already exist in src/process.rs.
• ProcessSpec::ansi_events moves parsing onto a bounded worker and emits ProcessEventKind::Ansi; raw pipe/LSP consumers retain their byte contract.
• AnsiParser is stateful across arbitrary feed boundaries, has a per-state escape-sequence cap, safely recovers malformed sequences, carries truecolor and underline color, and resets after finish().
• The parser currently emits Text, SetStyle, line-oriented controls, Erase, SetTitle, and alternate-screen markers. Cursor motion and most CSI/DEC operations are parsed but discarded by design.
• Alternate-screen suppression is currently parser-global and load-bearing for compile/REPL consumers. Vterm therefore requires an explicit parser profile: LineOriented preserves today's suppression and event contract; FullScreen emits all screen/mode operations. ProcessSpec selects the profile when ansi_events is enabled; existing Lua process specs default to LineOriented, while terminal sessions construct FullScreen specs.
• EditorState::tick_processes is the main-thread process drain point. LSP/MCP and Lua packages drain events only for process IDs they own.
• EditorCore::round_trip_buffers already disables optimistic frontend edits for special buffer-local input surfaces.
• Grid frontends already receive generic CellDelta; a terminal window can be composed into that grid without a new grid protocol.
• Semantic frontends hold document text through CRDT snapshots and receive byte-anchored style/decorations. They require a new terminal-specific message because an empty terminal identity buffer contains no screen text.
• Desktop persistence saves file-backed buffers only. A pathless terminal buffer is already omitted; no special persistence exception is required.

3. Terminal core model

3.1 Types and files

Stage 1 adds a src/terminal/ module rather than growing editor.rs or ansi.rs into a second monolith:

• screen.rs: TerminalScreen, TerminalGrid, TerminalRow, cursor, modes, scrollback, resize, snapshots;
• input.rs: normalized key/mouse/paste to VT byte encoding;
• session.rs: TerminalManager, TerminalSession, process ownership and event application;
• view.rs (stage 2): per-context viewport/selection helpers and TUI composition.

src/ansi.rs remains the one escape parser. It gains terminal operations; it does not depend on editor state or TerminalScreen.

The public core shape is:

pub struct TerminalManager { /* BufferId -> TerminalSession */ }

pub struct TerminalSelectionSpan {
    pub row: u32,
    pub start_col: u32, // inclusive
    pub end_col: u32,   // exclusive
}

pub enum TerminalProcessState {
    Running,
    Exited(i32),
    Signaled(String),
    Crashed(String),
}

pub struct TerminalSnapshot {
    pub buffer_id: BufferId,
    pub size: CellSize,
    pub cells: Vec<Cell>,       // row-major visible slice
    pub cursor: Option<CellCoord>,
    pub title: Option<String>,
    pub screen_generation: u64,
    pub selection: Vec<TerminalSelectionSpan>,
    pub scroll_offset: u32,
    pub at_bottom: bool,
    pub pid: u32,
    pub process: TerminalProcessState,
}

A snapshot is owned data taken only after all parser events for the current main-thread tick are applied. Renderers never borrow the mutable screen across Lua, editor-core, or process-supervisor calls.

3.2 Parser extension

AnsiEvent gains enough operations to drive a VT-style screen:

• printable text, BEL, CR, LF/VT/FF, BS, HT, and tab-stop set/clear;
• relative and absolute cursor movement (CUU/CUD/CUF/CUB, CNL/CPL, CHA/HPA, VPA, CUP/HVP);
• erase display/line/characters;
• insert/delete characters and lines;
• scroll up/down and set/reset scrolling margins;
• save/restore cursor for both DEC and CSI spellings;
• main/alternate screen enter/exit (47, 1047, 1049);
• mode set/reset for insert, origin, autowrap, application cursor, application keypad, cursor visibility, bracketed paste, focus reporting, synchronized output (?2026), and supported mouse reporting modes;
• SGR and title changes;
• DEC G0/G1 character-set selection plus SI/SO, including the line-drawing characters full-screen TUIs depend on;
• device-status/device-attribute queries represented as typed requests. The session, not the parser, writes bounded response bytes to PTY stdin.

Unknown, private, or malformed sequences stay non-fatal and bounded. Parser state always makes forward progress. DCS/APC/PM payloads remain ignored under the same per-sequence cap; they must not leak into visible text.

The parser-profile split is compatibility-critical. Full-screen support must not make compile-mode start appending alternate-screen text or receiving cursor events it does not understand. AnsiParser::new() and the existing Lua ansi = true process option retain the line-oriented profile; terminal session construction is the only initial full-screen caller. On finish(), LineOriented preserves today's synthetic alternate-screen/style balancing. FullScreen flushes pending text but does not invent an alternate-screen exit or clear cells. The session manager, after applying the actual final parser events, adds the process-exit annotation described in §4.1. Parser internals reset in both profiles.

The shared Cell::Style remains unchanged in this arc. Existing support covers indexed/truecolor foreground/background, bold, italic, underline variants, underline color, and reverse. Faint, conceal, blink, and strikethrough remain ignored rather than being mapped to an unrelated attribute. Extending the shared style would change every cell-carrying postcard encoding and is a separate protocol-wide decision, not hidden vterm scope.

3.3 Screen invariants

TerminalScreen maintains two grids:

• main screen with bounded scrollback;
• alternate screen with no scrollback and an independently saved cursor.

Every physical row records a monotonic logical-line ID, its cell offset within that logical line, and whether it ended in a soft autowrap. This is necessary for copy and resize: hard line breaks become \n; soft-wrapped physical rows are joined into one logical line. Per-view top/selection anchors use (line_id, cell_offset), not a physical row index, so reflow can remap them.

Core invariants:

• cells.len() == rows * cols; every row has exactly cols cells.
• Cursor and scrolling margins are always in bounds after every operation.
• A wide grapheme occupies a leading glyph plus Glyph::Continuation; an overwrite, erase, insert, delete, or resize never leaves an orphaned half.
• Combining codepoints extend the preceding grapheme when one exists; at the left edge they combine with a space cell. Cluster byte length is bounded.
• Autowrap uses the pending-wrap rule: writing the last column arms a wrap; the following printable grapheme performs it. Cursor motion/control clears the pending wrap where VT behavior requires.
• Origin mode interprets absolute row addressing relative to the active scrolling region.
• Insert/delete/scroll operations affect only their defined region and fill exposed cells with the current erase style.
• Entering 1049 saves the main cursor and clears the alternate grid; leaving it restores the main grid/cursor. Repeated set/reset is idempotent.
• Resizing the main screen reflows soft-wrapped logical lines, preserves hard breaks and logical-line IDs, and maps the cursor to the corresponding logical offset. The alternate screen is never reflowed: it is clipped/padded in place, matching a full-screen application's expectation that it will repaint after SIGWINCH.
• Scrollback eviction removes the oldest complete physical rows. It clamps a per-view anchor whose logical line was evicted to the oldest retained row. The default cap is 10,000 rows and an independent 4,000,000-cell budget; either limit may trigger eviction.

Synchronized output is a publication gate, not a second screen. Operations continue mutating TerminalScreen, but snapshots retain the last published generation until ?2026l. Exit/truncation releases the final state. A bounded one-second watchdog also releases and clears synchronization if a buggy child never resets it, preventing a permanently frozen editor surface.

Hard limits are shared constants, not frontend-local guesses:

• maximum rows: 512;
• maximum columns: 512;
• maximum visible cells: 262,144;
• maximum UTF-8 bytes in one grapheme cluster: 256;
• maximum retained history cells: 4,000,000;
• maximum parser control-string payload: the existing 1 KiB cap.

Invalid creation/resize arguments reject atomically. A rejected resize leaves the process and prior screen unchanged.

3.4 Device responses

The core responds to the small query set required by normal shells and TUIs:

• primary and secondary device attributes;
• operating-status report;
• cursor-position report, using current origin semantics.

Responses are fixed templates plus checked decimal coordinates and pass through the existing bounded write_stdin queue. OSC 52 clipboard writes, window manipulation, palette mutation, hyperlinks, sixel, and arbitrary DCS responses are not honored. Child output is untrusted; it cannot directly set the host clipboard or execute an editor command.

4. Session, buffer, and Lua contract

4.1 Session lifecycle

One terminal session owns exactly one process ID, one screen, and one identity buffer. A buffer may appear in several windows/frontends, but there is never a second parser or screen for it.

Creation order is transactional:

1. validate and copy the complete TerminalSpec;
2. create the read-only identity buffer;
3. spawn a raw PTY with ansi_events = FullScreen;
4. install the session in TerminalManager;
5. mark the buffer round-trip-only.

Stage 1 exposes that operation as a Rust manager contract for headless tests and future callers, but deliberately registers no interactive command: opening an unrenderable blank terminal buffer would be a broken partial feature. Stage 2's Lua binding calls the same operation and switches the caller's active window only after it succeeds. On synchronous spawn failure, the temporary buffer is removed and no session entry remains. The terminal process ID is not exposed through pmacs.process; only TerminalManager drains its events, so two consumers cannot steal batches from each other.

EditorState::tick_processes becomes:

1. supervisor tick();
2. terminal manager drains only its owned process IDs, applies all ANSI batches, queues device responses, and records terminal exit state;
3. the existing process.after-tick hook runs;
4. LSP/MCP retain their existing later ticks.

At process exit, final drained output is applied first. The manager then writes one synthetic, default-style hard line into the active terminal screen: Process <PID> exited normally with code 0 for zero; Process <PID> exited abnormally with code <code> for a non-zero code; or Process <PID> exited abnormally with signal <signal> for signal termination. It emits CRLF first when needed so the annotation never overwrites child text. The annotation is terminal-owned (not parser output and not rope text), visible and copyable like the rest of the screen. The buffer remains until the user kills it. Killing the buffer terminates a still-live process/session. A periodic prune handles all buffer-removal paths, including Lua callers that bypass the friendly terminal close API. Editor shutdown uses the existing supervisor shutdown path and cannot restart a terminal.

The wire-visible process state has only the four variants above: synchronous spawn failure never publishes a session, and terminate remains Running until the supervisor reports its final outcome. Crash/signal strings are sanitized to one line and bounded before snapshots or Lua metadata are built.

4.2 Buffer semantics

A terminal buffer is pathless, unmodified, and read-only. Read-only is a buffer-owned invariant, not only an intercept view: Buffer gains a flag and typed error checked by ordinary edits, intercept-skipping host edits, undo/ redo, and local/remote CRDT content mutation. The terminal manager sets it before publishing the session. The rope stays empty for the session lifetime.

Consequences are deliberate:

• buffer lists and window switching see a normal named buffer;
• normal save/autosave/LSP/syntax/CRDT editing does not apply;
• desktop save omits it because it has no file path;
• terminal scrollback does not participate in ordinary document search;
• copy reads from terminal rows, never from a hidden mirror rope;
• killing the buffer is the single editor-lifecycle teardown signal.

Semantic bootstrap may attach an immutable empty CRDT state and send its BufferSnapshot so v18/v19 mirrors can track the buffer identity and CursorByte without decode/state failure. No terminal contents enter that CRDT, and local/remote CRDT edit validation rejects the read-only buffer. The stage-3 terminal frame is the authoritative visible semantic surface; a forged remote operation cannot mutate the empty identity rope.

No hidden “text projection” is maintained. Two representations would drift on cursor rewrites, erase operations, alternate-screen swaps, and resize.

4.3 Lua API

Stage 2 constructs the shared TerminalManager immediately after the process supervisor, installs strict Rust primitives, then loads builtin/runtime/terminal.lua; all happen before LSP/MCP builtins and before user config. The Lua chunk owns friendly wrappers, the interactive command, buffer-local bindings, and the built-in statusline provider.

local buffer = pmacs.terminal.open {
  command = os.getenv('SHELL') or '/bin/sh',
  args = {},
  cwd = nil,                 -- inherits instance cwd
  env = {},
  name = nil,                -- default: *terminal:<command>*
  rows = 24,
  cols = 80,
  scrollback_rows = 10000,
}

pmacs.terminal.is_terminal(buffer)       -- boolean
pmacs.terminal.state(buffer)             -- fresh global metadata
pmacs.terminal.view_state(ctx)           -- fresh per-window metadata
pmacs.terminal.send(buffer, bytes)       -- explicit trusted raw bytes
pmacs.terminal.terminate(buffer)         -- SIGTERM; buffer remains
pmacs.terminal.scroll(lines)             -- boolean; interactive origin required
pmacs.terminal.scroll_to_bottom()        -- boolean; interactive origin required
pmacs.terminal.copy_selection()          -- boolean; interactive origin required

open accepts exactly the fields shown. It validates raw table fields before side effects: unknown fields, metatable-provided fields, holes in args, non-string environment keys/values, embedded NUL, non-integer dimensions, and out-of-range scrollback reject with the field named. The copied specification is immune to caller mutation. Returned and accepted identity is BufferIdLua, following the rest of the editor API.

Generated names are reserved against the live buffer registry before insert: *terminal:sh*, *terminal:sh*<2>, *terminal:sh*<3>, and so on. The lowest available suffix wins; failed creation consumes no suffix. An explicit name is preserved exactly after ordinary TerminalSpec validation.

state(buffer) returns a fresh plain table:

{
  buffer = buffer, pid = 123, rows = 24, cols = 80,
  title = nil, screen_generation = 7,
  process = { kind = "running" },
  -- or { kind="exited", code=0 },
  -- or { kind="signaled", signal="TERM" },
  -- or { kind="crashed", message="..." }
}

view_state(ctx) accepts the raw statusline context fields {frontend, window, buffer} and returns {at_bottom=boolean, scroll_offset=integer, selection=boolean}, or nil when that exact context is not a live terminal view. state/view_state expose no stored Lua tables, callbacks, or mutable manager state.

The three context-implicit view operations require a live authenticated interactive command origin. A plain programmatic pmacs.command.invoke outside such a dispatch does not synthesize one and raises a Lua error; so does an origin whose active window is not the addressed terminal context. Errors name the operation and leave view, selection, clipboard, and controller state unchanged. scroll(lines) requires an integer: positive moves toward older rows, negative toward the live tail, and zero returns false; otherwise it returns whether top changed. scroll_to_bottom() returns whether selection or top was cleared. copy_selection() returns true only when bytes were published and false for a valid terminal context with no selection.

There is deliberately no public Lua resize: the active controller's computed window content rectangle is the only geometry authority. send remains an explicit trusted escape hatch for packages and tests; ordinary user paste and keys use the mode-aware input path.

The built-in terminal command calls the public wrapper with $SHELL or /bin/sh, no shell-command interpolation, no string split, and no implicit sh -c. The wrapper installs terminal-buffer-local one-key commands: M-w copies, M-v/C-v page up/down, and M-</M-> move to the oldest retained row/bottom. They run only after the terminal escape prefix; normal terminal input sends those keys to the child.

4.4 Stage 2 view and controller contracts

Stage 2 adds src/terminal/view.rs. It is a projection over the one TerminalScreen, not another screen:

TerminalViewKey { frontend_id, window_id, buffer_id }
LogicalCellAnchor { logical_line_id, cell_offset }
TerminalSelection { anchor, head }          // inclusive display cells
TerminalViewState { top, selection, drag }  // keyed by TerminalViewKey
TerminalController { frontend_id, window_id }

cell_offset is the leading display-cell offset within one logical line. Clicks on a wide continuation canonicalize to its lead. Ordering is resolved against the current retained row sequence, not by comparing IDs. A top anchor resolves to the physical row containing that logical offset after reflow.

TerminalManager gains owned operations to register/retain/detach view keys, claim or release a session controller, create a snapshot_for_view(key, viewport_size), scroll/select/copy one view, and query fresh global/view metadata. detach_frontend and live-layout retention remove stale view/controller state; buffer prune removes every context for that session. The context-free Stage 1 snapshot(buffer) remains available for headless/core callers.

snapshot_for_view returns exactly viewport_size.area() cells for a nonzero valid viewport. At bottom it tail-aligns rows, padding above and to the right with default cells; a smaller view clips top/rows and right/columns. A scrolled view starts at its resolved top anchor and pads only after retained content is exhausted. Cursor and selection spans are translated into this returned coordinate space. scroll_offset is a saturating derived count of display rows between the viewport and live tail.

at_bottom is purely geometric: it is true exactly when scroll_offset == 0, meaning the live tail is currently visible. It is independent of the follow predicate (top == None && selection == None). Therefore a Shift-selection frozen at the tail has top != None, scroll_offset == 0, and at_bottom == true: the active cursor remains visible, unshifted supported child mouse reporting remains eligible, and the statusline emits no ↑0. The first later output retained behind that anchor makes scroll_offset > 0 and at_bottom == false.

Main-screen reflow keeps logical anchors stable. Beginning a selection freezes the current first visible row as top, even when it was the live tail, so later output has an anchor to preserve. Oldest-row eviction clamps a missing anchor once to the first surviving leading cell; a selection whose two ends collapse is cleared. Alternate-screen entry/exit or a reset that removes the referenced logical IDs clears affected selection/top state and returns the view to bottom. Child output follows only views with top=None and no selection.

5. Stage 2 — TUI integration

5.1 Composition, cursor, and status

RenderState::render_frame and paint_frame take an explicit target FrontendId. Layout lookup, statusline evaluation, active-window choice, and terminal view keys use that ID. A shared placement helper computes each window's outer rectangle, one-row modeline reservation, and content rectangle; both resize synchronization and painting consume the same result.

For every terminal buffer, the content rectangle is painted from snapshot_for_view instead of TextView::render. Cell glyph/style values are copied directly; no ANSI is reinterpreted. Line-number gutters, document wrapping, syntax, diagnostics, inlays, ordinary selections, and local/peer document overlays are suppressed for that window. Modeline/statusline, sibling splits, and cells outside the rectangle retain the existing pipeline.

Each (frontend_id, window_id, buffer_id) view follows §4.4. Merely rendering a passive view never resizes the PTY. Zero-area content is skipped without creating a view or changing the prior valid size.

The active terminal cursor is translated from snapshot-local coordinates into the content rectangle. It is hidden when the child hid it, the window is not the target frontend's active window, the viewport is scrolled from bottom, or the coordinate is clipped. Other terminal windows do not paint a cursor.

BEL is an out-of-band InstanceSignal::Bell only when a new bell occurs in the target frontend's active terminal. Historical bells are never replayed on later activation, and one bell count is delivered at most once per frontend. The in-process loop drains both clipboard and terminal signals and feeds them through Frontend::present_messages; the TUI Bell arm emits one host BEL. OSC title remains sanitized metadata (and a Stage 3 frame field). It never renames the identity buffer, injects host control bytes, or sets the host title.

terminal.lua registers a right-side provider named terminal, priority 10, face ui.modeline.terminal. It emits TERM while running, TERM:<code> on normal exit, TERM:<signal> on signal, or TERM:ERR on crash, and appends ↑<scroll_offset> only when scroll_offset > 0. An unset child face inherits the existing modeline foreground through the Arc 4 contract.

5.2 Input precedence and per-frontend dispatch

Stage 2 replaces the one pending KeyDispatcher with dispatch state keyed by FrontendId; keymaps and command registries remain shared. Terminal escape state is stored beside that dispatcher. dispatch_idle_for(frontend_id) uses the same frontend's pending prefix and active window; global modal surfaces still make every frontend non-idle while they own input.

EditorState carries an ephemeral authenticated command origin around key/menu/M-x interactive invocation and clears it with the invocation guard. Nested calls inherit that origin. Plain pmacs.command.invoke outside the guard neither stamps command history nor creates terminal view authority.

Input precedence is:

1. minibuffer, incremental search, completion/menu, query-replace, and other existing modal shadows;
2. that frontend's terminal escape-prefix state;
3. terminal key/mouse/paste handling when that frontend's active buffer is a terminal;
4. that frontend's ordinary buffer-local/global dispatcher and self-insert.

All terminal buffers stay in round_trip_buffers, so attached frontends reach this daemon-owned decision before optimistic edit. One user's pending escape or longer ordinary prefix cannot consume, cancel, or display as another user's pending sequence.

When terminal input owns a normalized key, terminal/input.rs encodes UTF-8 printable characters; Ctrl mappings and Alt ESC-prefixing; Enter, Tab, Backspace, Escape; arrows/Home/End according to application-cursor mode; Insert/Delete/Page, F1–F12, Shift-Tab, and supported modifier parameters. Unknown/lock/media keys are ignored. Press is actionable; local repeat is treated as another press and release is not forwarded. The normalized protocol cannot distinguish number-row from numeric-keypad characters, so application-keypad mode remains tracked but cannot transform them.

C-c is the fixed terminal escape prefix. It is consumed and makes the next key run through the same frontend's ordinary dispatcher; a resulting longer prefix stays in that frontend's dispatcher. C-c C-c instead sends literal Ctrl-C. Modal shadows consume their keys before either rule.

This is deliberately a consumed transport escape, not an Emacs-style C-c prefix map: the dispatcher receives the post-escape key as a fresh sequence, while C-c C-c is reserved for literal interrupt. Consequently a global or buffer-local binding whose first chord is C-c cannot fire in a terminal window. Packages may bind a post-escape one-key sequence, as the built-in terminal-local commands do. A configurable escape/prefix-map policy remains the named §11 deferral.

Paste sends exact bytes, wrapped in ESC[200~ / ESC[201~ only while the child enabled bracketed paste. It never passes through a shell or Lua. Authenticated focus gain claims the active terminal context and emits ESC[I when enabled. Focus loss emits ESC[O only when that source currently controls the session, then releases that controller; mode-off focus is silent.

5.3 Mouse, selection, copy, and scrollback

Child mouse reporting owns a pointer only when the exact terminal view is at bottom, the child enabled a supported tracking mode plus SGR encoding, and Shift is not held. Events inside the content rectangle translate to terminal-local 1-based cells; the active mode filters press, release, drag, move, and wheel.

Otherwise the editor owns the gesture:

• wheel scrolls that TerminalViewKey;
• primary drag stores inclusive logical-cell endpoints across history/screen;
• Shift is the explicit editor-selection override while child mouse reporting is active;
• an editor-owned right press follows the existing context-menu path;
• a new plain primary click clears the old selection before setting its anchor;
• child output does not move a scrolled viewport or selection.

Copy resolves anchors against retained logical rows, emits each leading glyph once, trims only trailing default blank cells, joins soft wraps without \n, and separates hard rows with \n. Wide continuations are never duplicated; combining clusters remain one UTF-8 sequence. Reversed drags normalize by retained row order. pmacs.terminal.copy_selection() writes through the existing kill-ring/clipboard setter for the acting frontend; ordinary document selection state is untouched.

Scrolling uses physical retained display rows and clamps at oldest/bottom. Reaching bottom clears top only when no selection is active. The explicit scroll_to_bottom/M-> action clears both selection and top so live-tail following resumes; ordinary copy leaves selection intact. Page commands use the current nonzero content-row count. Selection and scroll are available in the alternate screen only over its visible rows; no alternate output enters main history.

5.4 Durable control and resize

Each terminal session stores at most one TerminalController. Successful open claims the newly active (frontend, window). Later authenticated terminal key, paste, editor-owned/child-owned pointer, or focus gain claims the source's currently active terminal window. A render pass never claims control. Switching that controller away, killing its window/buffer, focus loss, or frontend detach releases it; size stays unchanged until another accepted context claims it.

Before the next terminal process drain and before paint, the instance synchronizes live terminal layouts. Only a controller whose exact window still shows that session may resize. Unchanged dimensions are suppressed before any PTY syscall. The manager validates once, performs resize_pty, then applies the same prevalidated TerminalScreen::resize in the same main-thread call; no supervisor output drain can interleave between them. A PTY failure leaves the prior screen geometry intact. The child may emit after SIGWINCH only on a later drain, when the screen already has the new geometry.

Content rows/columns come from the shared placement helper after modeline reservation and with no document gutter. A zero row/column result performs no resize and preserves the prior valid geometry. Passive splits/frontends only clip or pad their own snapshots.

5.5 Local and v18-daemon adapters

The in-process event adapter handles key press/repeat, mouse, paste, focus-gained/lost, and resize through the same EditorState terminal methods. It synchronizes layout before tick_processes, then presents pending clipboard/BEL messages. Host restoration remains the existing Frontend drop/error contract.

The daemon passes the authenticated connection source explicitly to grid render and input. Client-supplied IDs in v18 Key, Mouse, Paste, Focus, Resize, and Detach payloads never choose a view or controller. Session detach removes that frontend's dispatcher, terminal views, controller claims, and bell baseline. These are Stage 2 changes to existing v18 grid behavior; no protocol bump or semantic/GPU terminal surface is added in this PR.

One intentional Stage 2 boundary remains until Stage 3: an authenticated v18 semantic frontend can send a key while its active buffer is a terminal, claim that terminal's controller, and feed the PTY, but cannot display the screen. The next accepted TUI terminal input reclaims control; v19 removes the invisible interval by adding the semantic terminal surface.

6. Stage 3 — protocol v19 and GPU integration

6.1 Protocol-owned wire contract

Protocol v19 appends, never inserts, one instance message and two frontend events after the final v18 variants:

#[derive(Clone, Debug, Eq, PartialEq, Serialize, Deserialize)]
pub struct TerminalFrame {
    pub buffer_id: BufferId,
    pub size: CellSize,
    pub cells: Vec<Cell>,
    pub cursor: Option<CellCoord>,
    pub title: Option<String>,
    pub screen_generation: u64,
    pub selection: Vec<TerminalSelectionSpan>,
    pub scroll_offset: u32,
    pub at_bottom: bool,
    pub pid: u32,
    pub process: TerminalProcessState,
}

InstanceMessage::TerminalFrame(TerminalFrame)

FrontendEvent::TerminalResize {
    frontend_id: FrontendId,
    buffer_id: BufferId,
    size: CellSize,
}

FrontendEvent::TerminalPointer {
    frontend_id: FrontendId,
    buffer_id: BufferId,
    coord: CellCoord,
    kind: MouseKind,
    mods: Modifiers,
}

TerminalProcessState, TerminalSelectionSpan, and every limit needed to validate these values move to or are re-exported from pmacs-protocol; core paths may re-export them so Stage 1/2 callers do not gain duplicate types. The shared limits are the landed row, column, visible-cell, grapheme, and metadata bounds plus:

pub const MAX_TERMINAL_FRAME_GLYPH_BYTES: usize = 8 * 1024 * 1024;

The aggregate counts each Char's UTF-8 length, every Cluster byte, and zero for Continuation, with checked addition. TerminalFrame::validate is the single structural policy used before daemon emission and after GPU decode. pmacs-protocol takes the direct unicode-width dependency needed to validate one/two-column glyph and continuation topology; another frontend must not copy that policy.

The existing MAX_FRAME_BYTES = 16 MiB remains unchanged. A protocol test constructs the maximum row/column frame with one maximal legal selection span per row and maximum title/process metadata. Every cell carries a legal one-column Cluster plus the maximal-encoding legal Style: RGB foreground, background, and underline color, a non-None underline, and all boolean flags set. The fixture distributes the exact aggregate budget across a legal cluster in every cell and chooses cluster lengths to maximize total serialized length-prefix overhead rather than packing bytes into a few maximal clusters. This maximizes cluster and per-cell style overhead together. It serializes the enclosing InstanceMessage with postcard::to_allocvec and asserts the measured length is below MAX_FRAME_BYTES. A one-byte-over aggregate is rejected before serialization. This is a wire-specific bound, not a mutation of the TUI screen: if a child constructs a larger internal snapshot, the semantic producer retains its last valid baseline, emits nothing malformed or truncated, and logs the first distinct bounded error until a valid frame clears the latch.

TerminalFrame is a complete visible-grid replacement. Empty is not a clear sentinel: valid terminal dimensions are nonzero and cells.len() equals the checked area exactly. screen_generation describes the published terminal screen/title generation; selection, scroll, viewport, and process state may change without it. The producer compares every ordered field against one retained baseline per semantic frontend context. A view-only change therefore sends; a byte-identical/equal payload is silent. Buffer snapshot, detach, and context replacement clear that baseline so the next valid terminal frame is authoritative.

Validation is atomic and covers:

• shared nonzero row/column/checked-area and aggregate-glyph limits;
• exact cell area; each caller separately requires the expected current buffer_id;
• cursor bounds;
• title and process-state metadata length/control-character rules;
• valid nonempty cluster UTF-8 within the per-cluster limit;
• printable one/two-column leading glyphs, required wide continuations, and no orphan continuation; continuation style is ignored in favor of its lead;
• no Attachment in any terminal cell;
• strictly increasing, one-per-row, nonempty selection spans inside the frame;
• at_bottom == (scroll_offset == 0).

Invalid daemon output is never written. Invalid GPU input retains the previous valid frame, requests no redraw, and reports one latched diagnostic rather than partially applying cells or metadata.

Compatibility remains additive:

• v18 grid peers keep receiving the Stage 2 composed CellDelta terminal windows;
• v18 semantic peers receive the immutable empty identity snapshot but no terminal message. Terminal use remains unsupported and invisible for those peers; ordinary document editing remains supported;
• v19 frontends send TerminalResize/TerminalPointer only to a negotiated v19 daemon;
• the v19 daemon filters TerminalFrame from every wire below v19;
• postcard pins preserve every v18 discriminant and pin all three appended v19 discriminants.

6.2 First-frame bootstrap and authenticated routing

BufferSnapshot remains the one semantic display-switch message. It carries the terminal identity buffer's valid empty CRDT state and adds no terminal flag. Immediately after applying any snapshot, a v19 GPU sends the existing Viewport for the new replica/generation and, when its derived terminal content rectangle has at least one row and column, TerminalResize with the new buffer_id and size in cells. A zero-area window sends no terminal declaration until a later geometry change yields a valid size.

The daemon authenticates the connection source before reading any claimed frontend_id. A document buffer accepts only Viewport; an active terminal buffer accepts only TerminalResize. The inapplicable declaration is dropped without mutation or logging noise. This dual declaration occurs only after a snapshot or an actual geometry change, not every frame, and removes the otherwise circular dependency where the GPU would need a terminal frame before it knew to request one.

For an authenticated active terminal window, a valid TerminalResize always records that exact (frontend, window, buffer) view size so passive frontends can receive their own clipped/padded projection. It resizes the PTY only when that exact view is the durable controller from §5.4; resize never claims control. The semantic adapter consumes a content CellSize directly and does not run the TUI placement helper or subtract a modeline again. Unchanged, zero/out-of-range, passive, and failed resizes retain existing geometry under the Stage 2 ordering contract.

TerminalPointer must match the authenticated source, active terminal buffer, and last accepted terminal viewport, and its coordinate must be in bounds. Once accepted, it follows the same Stage 2 terminal pointer path: child SGR mouse reporting when eligible, otherwise per-view scroll/selection/context menu. Like other accepted pointer/input/focus events, it may claim control. A forged source, stale buffer, missing declaration, or out-of-bounds coordinate is dropped before view, controller, selection, menu, or PTY mutation.

Key, paste, focus, detach, BEL, and clipboard keep their landed event/message types. The daemon continues to overwrite client-claimed IDs with the authenticated source before terminal dispatch. Terminal mode adds no raw-byte input message and never sends child bytes through Lua or a shell.

6.3 Semantic producer and editor adapters

SemanticRenderState stores the optional terminal viewport and last valid terminal-frame baseline for its one authenticated frontend. When the active buffer is terminal and a matching viewport exists, it requests an owned snapshot for the exact active TerminalViewKey, validates/converts it, and emits TerminalFrame only on complete-payload change.

The editor-side contract is narrow:

prepare_semantic_terminal_view(
    frontend_id: FrontendId,
    buffer_id: BufferId,
    size: CellSize,
) -> Option<TerminalSnapshot>

sync_semantic_terminal_layout(
    frontend_id: FrontendId,
    buffer_id: BufferId,
    size: CellSize,
) -> bool

dispatch_semantic_terminal_pointer(
    frontend_id: FrontendId,
    buffer_id: BufferId,
    size: CellSize,
    coord: CellCoord,
    kind: MouseKind,
    mods: Modifiers,
) -> bool

Each method derives the active WindowId from frontend_id, verifies that it still displays buffer_id, and delegates to the existing manager/view/input state machines. No method accepts a client-supplied window identity. Semantic layout sync runs after event coalescing, before tick_processes, exactly beside the landed grid sync; snapshot production occurs on the following render pass from the already-published screen.

The terminal producer retains the buffer-independent/UI messages required by the native frontend: StatusFacts, ThemeFacts, FontFacts, StatuslineSegments, MenuPrompt, and MinibufferPrompt, plus daemon-owned DispatchIdle, Signal, and lifecycle messages. The built-in terminal statusline provider therefore remains the source of title/process/scroll text. It suppresses document-only style spans, decorations, inlays, block adornments, folds, file summaries, search/completion surfaces, line numbers, document CursorByte, and presence for the terminal identity buffer.

On terminal activation the GPU clears/ignores every document-local visual cache before painting the first frame. On switching back, snapshot reset clears the producer's document baselines so the first matching document viewport receives the existing full authoritative style/decoration/summary resync. Terminal baselines are per frontend context; one split/frontend can never suppress or overwrite another's scroll/selection projection.

6.4 GPU state and fixed-cell renderer

The GPU state machine is explicit: Document or Terminal { buffer_id, frame, derived paint caches }. BufferSnapshot immediately leaves terminal mode, clears the prior terminal frame and terminal-only caches, and restores document defaults. A valid matching TerminalFrame enters terminal mode. A stale-buffer frame is ignored; an identical valid frame is retained without rebuild or redraw.

Terminal geometry is the drawable code rectangle above the existing status band, with no document gutter or minimap. Rows and columns are floor(pixel_extent / active_cell_metric), clamped through the shared nonzero protocol limits. Pixels, scale, DPI, and glyph advances never cross the wire. Rows never wrap; excess frame rows/columns clip to the declared cell rectangle and undersized content is padded with terminal defaults.

Painting is cell-derived rather than rope-derived:

• Every cell rectangle has a fixed origin from (row, col) and the active monospace metrics. Backgrounds coalesce only adjacent equal resolved colors.
• Default foreground/background map to the GPU's existing plain-text/window defaults; indexed colors use the existing xterm palette; truecolor is exact. reverse swaps the two resolved colors. A continuation draws no glyph and inherits its lead cell's paint semantics.
• Text shaping is split into explicitly positioned row runs. Contiguous single-width ASCII may share one monospace buffer with rich attribute spans; non-ASCII/cluster/wide leads start at an explicit cell origin and are clipped to their declared one/two-cell footprint. A shaped advance never chooses the next run's column.
• Bold and italic use font attributes. Single/double/dotted/dashed underlines use fixed-cell quads; curly uses the existing squiggle pipeline. Default underline color follows the post-reverse foreground.
• Terminal selection is a separate fixed-cell wash resolved through the existing GPU ui.selection site; it never rewrites child cell styles. Cursor visibility/position comes only from the frame and paints through the existing caret primitive inside the terminal clip.
• The status band and its provider runs remain outside/above terminal paint. Document decoration, presence, caret, gutter, and minimap batches are not prepared or drawn in terminal mode.

6.5 GPU input, signals, and cache invalidation

Keyboard, paste, focus, and detach reuse existing attach messages and daemon encoding. Inside the terminal clip, GPU mouse hit testing is pixel-to-CellCoord; press/release/drag/move/wheel sends TerminalPointer instead of a source-byte Pointer. The status band/outside clip is never a terminal hit. Move/drag events coalesce only while kind, coordinate, and modifiers are unchanged.

Window resize, scale change, accepted FontFacts, and buffer snapshot recompute the cell viewport. One changed size sends one version-gated TerminalResize; an equal size is silent. A font change clears terminal shape and geometry caches until a matching-size authoritative frame arrives.

Invalidation is deliberately narrow:

• a changed terminal frame rebuilds cell text/background/underline/selection/ cursor data, but not statusline buffers;
• ThemeFacts rebuilds the selection/status color sites, not child cell shaping;
• FontFacts rebuilds shape and geometry and emits a changed cell viewport;
• status/statusline/menu/minibuffer messages touch only their existing caches;
• a duplicate valid terminal frame and an unchanged geometry declaration do no work.

InstanceSignal::Bell requests one frontend attention event for each new active-terminal BEL; historical/passive suppression remains daemon-owned. InstanceSignal::Clipboard keeps the existing OS clipboard path. OSC title is sanitized frame/statusline metadata only and never becomes a raw window-title or terminal-control operation.

7. Four-agent execution plan

The vterm roster is fixed at four agents for all three stages. Do not add review/scout agents; reuse these owners so state-machine decisions stay coherent.

Owner	Stable scope	Primary files
Lead/integrator	contracts first; Stage 1/2 manager/Lua lifecycle; Stage 3 semantic producer, authenticated daemon routing, shared acceptance, gates, docs, branches/PRs	src/terminal/session.rs, src/lua_bindings/mod.rs, builtin/runtime/terminal.lua, src/semantic_render.rs, owned Stage 3 sections of src/daemon.rs, tests/vterm_*_acceptance.rs, docs
VT core agent	encoder/screen seams; Stage 3 snapshot-to-wire conversion and shared terminal re-exports, no renderer ownership	src/ansi.rs, src/terminal/{screen,input,session,view}.rs in assigned non-overlapping sections
TUI agent	landed TUI projection/input; Stage 3 exact active-window semantic adapters and parity tests, no GPU/protocol files	owned sections of src/editor.rs, focused TUI/adapter tests
Protocol/GPU agent	protocol v19 types/limits/pins/gates and native GPU state/render/hit-test/attach sending	pmacs-protocol, src/protocol.rs, pmacs-gpu/src/{main,attach}.rs

Coordination rules:

• Lead establishes invariants and method signatures before another lane edits callers; the protocol/GPU agent then implements the shared wire types.
• Strict Stage 3 file ownership follows the table. VT-core and TUI edits in src/terminal/{session,view}.rs / src/editor.rs are agreed as exact non-overlapping symbols before work starts. Only the lead edits src/semantic_render.rs, Stage 3 daemon routing, or shared acceptance. Stage 3 begins only from landed Stage 2.
• Workers do not update docs, ledgers, branches, or PRs and do not stash, checkout, rebase, or merge.
• Workers add focused tests in owned modules. Lead alone owns shared acceptance files.
• Exact-path staging only; never git add ..
• Four agents are the total vterm team, not four implementation workers plus a lead.

Per-stage utilization:

• Stage 1: completed by lead + VT core; TUI and protocol/GPU reviewed future consumer contracts.
• Stage 2: lead establishes manager/Lua contracts and authenticated adapters; TUI implements projection/input/rendering; VT core adds only required encoder/query corrections; protocol/GPU checks snapshot neutrality.
• Stage 3: lead locks the protocol constants/types and editor method signatures, then owns src/semantic_render.rs, authenticated src/daemon.rs routing, shared acceptance, and integration. The protocol/GPU agent owns pmacs-protocol plus pmacs-gpu/src/{main,attach}.rs; the VT-core agent owns snapshot-to-wire conversion/shared terminal re-exports; the TUI agent owns the exact semantic adapters in src/editor.rs and parity tests. All four run in parallel only after the lead's contract checkpoint; no TUI rendering behavior changes.

8. Branch and PR plan

Stage 1 landed as PR #126 at merge 643d1e1. Stage 2 landed as PR #130 at merge 86fc1bc. Revision 8 is preserved for approval on vterm-stage3-framing, based on the integrated current main.

After explicit framing approval:

1. create worktree pmacs-vterm-gpu and branch vterm-gpu from the then-current canonical githubsucks/main;
2. implement only Stage 3 / criteria 28–37;
3. run the complete sequential gate and bite suite;
4. open the third and final vterm PR for user review; never merge it without explicit authorization.

The historical framing branch vterm-framing remains the Revision 7 record. The Stage 3 implementation is not stacked on a documentation branch or an unmerged feature parent.

9. Acceptance

Stage 1 — terminal core

1. Feed every supported CSI/OSC/DEC sequence, including IND/NEL/RI, at every byte split; whole-feed and split-feed screens are identical. RI and forward-index operations additionally pin exact scrolling-margin behavior.
2. Split UTF-8, malformed UTF-8, truncated escape, over-cap control string, and unknown private sequences recover without panic, unbounded growth, or visible escape leakage.
3. Cursor absolute/relative movement, save/restore, origin mode, margins, insert/delete character/line, erase, and scroll mutate only the specified cells.
4. Autowrap pending state, wide glyphs, combining clusters, overwrite, erase, and clipping never create orphan continuations.
5. Main/alternate screen swaps preserve the main grid and cursor; alternate output never enters scrollback. Synchronized output publishes no intermediate frame and releases on reset, EOF, and watchdog expiry.
6. DEC line drawing through G0/G1 + SI/SO renders the expected Unicode box glyphs across split feeds.
7. SGR indexed/truecolor/underline/reverse survives screen operations; ignored attributes leave supported fields unchanged.
8. Main-screen resize reflows only soft wraps, preserves cursor/logical-line identity and application tab stops, and adds defaults only in new columns; alternate-screen resize clips/pads without reflow.
9. Scrollback obeys both row and cell budgets, evicts oldest rows, and keeps the visible grid exact.
10. DA/DSR/CPR query events produce bounded exact response bytes; unsupported OSC/DCS cannot write stdin or clipboard.
11. Strict owned TerminalSpec values reject before spawn and are mutation-independent after spawn.
12. A real PTY child prints cursor-addressed/alternate-screen content in adversarial chunks; final output lands first, then exact normal/non-zero/ signal process annotations are visible and copyable before exit state.
13. Spawn failure leaves no buffer/session/process residue. Killing a live terminal buffer terminates it; editor shutdown leaves no child/reader.
14. Every rope mutation path (ordinary, intercept-skipping, undo/redo, local or remote CRDT edit/import) rejects the read-only terminal buffer and leaves its rope/revision/modified state unchanged; immutable empty CRDT bootstrap remains valid.

Stage 2 — TUI

15. Lua open enforces the strict owned table contract, uniquifies generated names without consuming failed suffixes, publishes no partial state on error, and switches/claims the active window only after success. state and view_state return exact fresh plain tables; no public Lua resize bypass exists. Context-implicit view operations error without an authenticated interactive terminal origin and otherwise return the exact changed/copied booleans without partial mutation.
16. A terminal window paints exact cells/styles inside its content rectangle; top/right padding, clipping, modeline, sibling splits, outside cells, and suppression of document/peer overlays are exact and control-free.
17. Per-context snapshots preserve logical top/selection anchors through main-screen reflow, derive the correct scroll offset, clamp oldest-row eviction once, and clear invalid alternate/reset anchors. A selection frozen at the live tail pins top != None, scroll_offset == 0, and at_bottom == true; cursor, child-mouse eligibility, status suffix, and the first subsequent output transition follow that definition exactly.
18. Printable, Ctrl, Alt, navigation/function keys, application cursor, focus, unknown keys, and paste produce exact PTY bytes; bracketed wrappers appear only when enabled.
19. C-c dispatches one fresh editor key and retains the owning frontend through a longer prefix; C-c C-c sends Ctrl-C. Ordinary bindings whose first chord is C-c are deliberately unreachable in terminal windows. Two frontends cannot consume one another's escape/pending state or dispatch-idle value, and existing modal shadows remain authoritative.
20. Supported SGR mouse modes receive translated reports only at bottom without Shift. Mode-off, scrolled, unsupported-legacy, and Shift gestures remain editor-owned; wheel, drag, clear, and right-context behavior write no PTY bytes.
21. Copy handles soft/hard wraps, trailing blanks, wide/combining glyphs, reversed drags, resize/reflow, eviction, alternate screen, and history/screen crossings exactly once, then publishes to the acting frontend's kill-ring/clipboard path without touching document selection.
22. The durable authenticated controller alone resizes. Open/input/focus claims and focus/switch/kill/detach releases are exact; unchanged, zero, passive, and failed resize cases preserve prior geometry without thrash, and screen resize precedes the next child-output drain.
23. Forged v18 grid payload frontend IDs for key, mouse, paste, focus, resize, or detach cannot select or affect another frontend's terminal context. Detach and layout retention remove only the matching views, dispatcher, controller, and bell baseline.
24. Local and daemon-grid paths deliver clipboard and each new active-terminal BEL exactly once. Historical/passive bells and OSC titles do not become host control effects. The built-in terminal provider reports exact process/scroll state for each split.
25. Two frontends and sibling splits over one terminal retain independent bottom/scroll/selection snapshots while sharing one process, screen, title, process outcome, and controller.
26. Killing the identity buffer terminates/reaps the child and removes all views; switching away leaves it running; editor/drop and error paths restore the host terminal and leak no child, reader, or stale round-trip state.
27. A hermetic real TUI smoke opens /bin/sh, runs a cursor-addressed probe, exercises key/paste, resize, scroll/select/copy, BEL, and clean exit, then proves host raw/alternate-screen state is restored.

Stage 2 verification map

The cross-surface suite is tests/vterm_stage2_acceptance.rs; focused unit coverage remains beside the owning implementation. The criteria map as follows:

• 15: lua_surface_is_strict_fresh_transactional_and_context_safe.
• 16: editor::tests::terminal_snapshot_composes_only_content_and_translates_cursor plus the real-TUI smoke.
• 17: terminal::view::tests::{tail_projection_pads_above_and_right_and_translates_cursor, frozen_top_is_geometrically_at_bottom_when_view_still_reaches_tail, alternate_switch_clears_view_anchors_and_selection} and shared_screen_keeps_view_scroll_selection_and_controller_independent.
• 18: terminal::input::tests::{utf8_ctrl_and_alt_boundaries, application_cursor_and_xterm_modifiers, ambiguous_digits_ignore_application_keypad, paste_and_focus_are_exact, unsupported_keys_are_invisible} and the real-TUI input/paste path.
• 19: editor::tests::dispatch_prefix_state_is_independent_per_frontend, terminal_escape_gates_local_bindings_and_double_escape_sends_interrupt, lua_surface_is_strict_fresh_transactional_and_context_safe, and the real-TUI escaped editor-binding/quit path.
• 20: terminal::input::tests::sgr_mouse_modes_modifiers_and_coordinates plus the real-TUI editor-owned scroll/drag/copy path.
• 21: terminal::view::tests::{copy_joins_soft_wraps_trims_default_blanks_and_separates_hard_rows, wide_continuation_canonicalizes_to_lead_and_copies_once}, lua_surface_is_strict_fresh_transactional_and_context_safe, and the real OSC 52 clipboard assertion.
• 22: lua_surface_is_strict_fresh_transactional_and_context_safe, shared_screen_keeps_view_scroll_selection_and_controller_independent, and the real child-PTY resize assertion.
• 23: daemon::tests::forged_resize_mutates_only_the_authenticated_frontend, daemon::tests::inbound_paste_uses_authenticated_source_not_the_claimed_id, the existing m5_4_dispatch_{key,mouse}_threads_frontend_id_to_lua_surface tests, and the multi-frontend detach assertions in shared_screen_keeps_view_scroll_selection_and_controller_independent.
• 24: the built-in-provider and clipboard assertions in lua_surface_is_strict_fresh_transactional_and_context_safe, daemon::tests::terminal_bell_baseline_suppresses_history_and_delivers_each_new_bell_once, and the real-TUI BEL/OSC 52 assertions.
• 25: shared_screen_keeps_view_scroll_selection_and_controller_independent.
• 26: both in-process acceptance tests' termination/cleanup assertions and the real-TUI clean-exit/host-restoration assertions.
• 27: real_tui_terminal_smoke_restores_host_after_output_input_resize_scroll_copy_and_bell.

Stage 3 — GPU/protocol

28. Protocol v19 appends all three new variants after the v18 pins; v18 grid traffic round-trips byte-identically, v18 semantic document traffic still works, and both outbound directions are independently version-gated.
29. The measured maximum legal frame uses maximum dimensions, one maximum selection span per row, maximum metadata, the exact aggregate glyph budget present as one legal cluster per cell with lengths chosen to maximize serialized length-prefix overhead, and the maximal-encoding legal style on every cell. Its enclosing message encodes below the unchanged 16 MiB transport cap. Validation accepts exact shared boundaries and atomically rejects one-byte-over aggregate, over-area, bad area, out-of-bounds cursor, control/malformed/overlong clusters, orphan/missing continuations, attachments, duplicate/out-of-order-row or otherwise invalid selection spans, inconsistent bottom state, overlong title, and overlong process text while retaining the prior valid frame.
30. First terminal activation emits one authoritative complete frame after the dual viewport declaration, then stays silent for a completely equal payload. View-only and process-only changes emit despite an unchanged screen generation. Terminal activation suppresses document projection, cursor, presence, gutter, and completion; switching back forces one complete document resync.
31. Two semantic frontends over one terminal receive independent sizes, scroll, selection, cursor visibility, and baselines while sharing one process/screen. A passive declaration produces its clipped/padded frame but does not resize; only the exact durable controller changes PTY geometry.
32. Forged frontend/buffer IDs, stale buffers, undeclared viewports, and out-of-bounds terminal pointer/resize events cannot affect another view, controller, terminal selection, menu, PTY size, or child input.
33. Headless GPU rendering pins default/indexed/truecolor foreground and background, reverse, bold/italic, all supported underline forms, wide and combining footprints, continuation inheritance, selection, cursor, padding/clipping, status-band separation, and absence of frontend wrapping, document gutter/minimap, and document overlays.
34. GPU key, paste, focus, press/release/drag/move/wheel input reaches the same Stage 2 terminal encoders and ownership paths. Pixel hit testing yields only in-bounds cells, never source bytes or wire pixels, and unchanged move/drag cells coalesce.
35. Buffer/window/scale/font transitions emit exactly one changed cell declaration and suppress identical sizes. Terminal, theme, font, and statusline changes invalidate only their named caches; duplicate valid frames request no redraw.
36. Each new active BEL produces one GPU attention action. Terminal copy publishes through InstanceSignal::Clipboard and the existing OS clipboard path exactly once. Sanitized OSC title/process/scroll metadata reaches the terminal provider/statusline without becoming a raw host-title or control effect.
37. A hermetic real daemon + required headless GPU smoke opens /bin/sh, runs a full-screen alternate-screen probe, exercises key/paste/mouse/resize, BEL/title metadata, scroll/select/copy through the clipboard signal, clean exit, and buffer switch-back, then proves the preserved main screen and all child/reader/session cleanup.

Stage 3 verification map

The cross-surface suite is tests/vterm_stage3_acceptance.rs; focused wire and GPU assertions remain in pmacs-protocol and pmacs-gpu respectively.

• 28–29: postcard discriminant/round-trip pins, common TerminalFrame::validate boundary table, measured maximum legal payload, and v18/v19 daemon/frontend send filters.
• 30–32: semantic producer baseline/reset tests, dual-declaration bootstrap, real dispatcher source-forgery tests, and two-frontend controller/passive-view acceptance.
• 33: pure fixed-cell paint-plan tests plus required headless offscreen pixel probes for representative color/style/wide/selection/cursor/clipping cases.
• 34–36: attach/event coalescing tests, authenticated daemon input tests, and headless signal/statusline observations.
• 37: one real-daemon/real-PTY/headless-wgpu acceptance path; it is not replaced by a decoded-message fixture.

10. Gates and bite verification

Every PR runs the standing full gates from AGENTS.md, sequentially, plus its stage acceptance suite. Stage 2 included a real hermetic TUI PTY smoke. Stage 3 adds cargo test --test vterm_stage3_acceptance, its CRDT variant, PMACS_REQUIRE_GPU=1 cargo test -p pmacs-gpu, the real-daemon/headless-GPU probe, and the ordinary workspace sweep.

New behavioral acceptance must be bite-verified against the immediate pre-stage tree with scripts/bite where the swapped files compile. Protocol v19 tests additionally pin postcard bytes, prove the measured aggregate-bound maximum stays below the unchanged transport cap, and verify both older-version send filters; a test that merely fails to decode on old code is not a useful bite.

11. Explicit deferrals

Not part of these three PRs:

• terminal image protocols (sixel, kitty graphics, iTerm images);
• OSC 8 hyperlink interaction;
• faint, blink, conceal, and strikethrough additions to shared Style;
• kitty keyboard protocol, key release events, media keys, and IME preedit;
• cursor-shape/blink rendering and numeric-keypad distinction absent from the current normalized input/cursor protocol;
• RIS (ESC c), DECALN (ESC # 8), and DEC cursor save/restore mode ?1048;
• CUU/CUD region clamping when the cursor starts inside scroll margins while origin mode is disabled;
• combining a character into the preceding cell across intervening SGR or cursor-control events;
• DECSTBM clamping when an explicit bottom margin exceeds the current screen height; the current core leaves the existing scrolling region unchanged;
• exact xterm ?1047 clear-on-exit and scroll-margin preservation across alternate-screen switches;
• legacy X10 mouse byte encoding when a child enables mouse tracking without SGR mode; Stage 2 sends no report for that unsupported combination;
• bracketed-paste payload filtering: Stage 2 forwards exact paste bytes as framed, so embedded ESC[201~ can terminate the wrapper early; xterm-style filtering/escaping requires a separate input-policy decision;
• nonstandard CSI 3 K ignore semantics (the current core clears the line);
• the ASCII fast path that avoids grapheme-candidate allocation and segmentation for every printable character after another ASCII character, and avoiding the per-sequence intermediates clone in CSI dispatch;
• cleanup of the defensive impossible-state path where a terminal spawn returns a process without a running PID, and borrow-tolerant EditorState drop; normal spawn/rollback/prune/shutdown paths remain covered;
• a separately named configuration-time scrollback-row cap; the current validation conservatively reuses the history-cell cap before the runtime row and cell budgets enforce the effective limit;
• shell integration, prompt marks, command semantic zones, and cwd reporting;
• ordinary document search over terminal history;
• terminal session persistence/reconnect across editor restart;
• reparenting a live terminal process into a second daemon instance;
• user-configurable escape key and scrollback policy.

Deferral means graceful ignore or documented absence, never escape leakage, panic, unbounded allocation, or child leak.

12. Resolved decisions

The 2026-07-22 architecture, re-scout, and final framing review resolved every current question:

1. Fixed terminal editor escape: C-c; C-c C-c sends literal Ctrl-C.
2. Resize: reflow main-screen soft wraps; clip/pad alternate screen.
3. Exit: retain the buffer and append the process PID/outcome line from §4.1.
4. Compatibility: additive v19; v18 grid remains supported, v18 semantic has no terminal surface.
5. GPU wire: complete visible frames with complete-payload suppression under one shared 8 MiB aggregate glyph-byte bound; the 16 MiB transport cap stays.
6. Style: preserve the shared encoding and defer unsupported attributes.
7. Identity: one process/screen per terminal BufferId.
8. View state: logical-line/cell anchors per (FrontendId, WindowId, BufferId); at_bottom means scroll_offset == 0, while following additionally requires no top anchor and no selection; no second screen.
9. Control: the most recently authenticated accepted terminal context owns resize until focus/switch/kill/detach releases it; render never claims.
10. Dispatch: terminal escape and ordinary pending prefixes are per frontend; the consumed C-c escape deliberately hides ordinary C-c-leading bindings in terminal windows.
11. Mouse: Shift or scrollback forces editor selection; supported SGR child reporting owns unshifted at-bottom gestures.
12. Resize order: validate, suppress unchanged, resize PTY, resize the screen before any subsequent child-output drain; failure preserves old geometry.
13. Lua: strict open/state/view/send/terminate/scroll/copy surface; no public geometry bypass; implicit view operations require authenticated interactive origin and otherwise error without mutation.
14. Host effects: clipboard and BEL use explicit frontend signals; OSC title remains sanitized metadata.
15. Bootstrap: after every semantic snapshot, v19 sends both byte viewport and terminal cell size; the authenticated daemon accepts only the declaration matching the active buffer kind.
16. Semantic resize: the declaration records passive view geometry, but only the exact durable controller changes the shared PTY/screen size.
17. GPU layout: fixed cell rectangles own geometry and hit testing; shaped glyph advances never determine subsequent columns, and OSC title remains metadata rather than a host control effect.