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Theme faces — framing (Arc 4 stage 1, themes)

Revision 5 — 2026-07-14. Status: implemented on branch theme-faces (PR #120); revision 5 folds PR round 1.

Revision 5 (PR #120 round 1, findings 1–4): accepting a FileStyleSummary on the GPU now drops the cached minimap vertices — theme recolors and diagnostic republishes arrive at an UNCHANGED generation, and the cache keys only on (generation, dims, scroll), so the stale strokes survived until an edit/resize/scroll; the daemon's payload-equality suppression makes the invalidation precise (finding 1). lua_to_style propagates every Table::get error: the lookups run __index, so a raising metatable previously parsed as an all-default style and the merge SUCCEEDED, committing its valid siblings against the Q#TH6 all-or-nothing contract; boolean fields deliberately keep Lua truthiness (mlua's bool), so only lookups that RAISE fail the transaction (finding 2). The producer is peer-version-aware: SemanticRenderState::for_peer records whether the peer negotiated >= 16, and below that no ThemeFacts is produced at all AND no ui.diag.* face is folded into the FileStyleSummary marks — that summary is an ungated pre-v16 channel, and a v15 peer must not get face-derived minimap colors while its squiggles, signs, and counters stay unthemed; the summary's cache key zeroes its face-epoch component for such peers so face edits don't trigger pointless whole-file recomputes (finding 3). And the "canonical severity color" claim is weakened to what is true: the daemon-RESOLVED color is canonical (TUI squiggle/marker/minimap and, when a face is set, all GPU surfaces), but the GPU's BUILT-IN defaults — bright RGB constants for squiggles/signs/counters vs the minimap's converted Indexed(1/3/6/8) — are a pre-existing divergence this arc keeps, because unset faces must render byte-identically to before (finding 4).

Revision 4 (framing round 3, findings 1–7): ui.minibuffer.candidate now has a real GPU site: its fg colors the existing minibuffer-dropdown candidate glyph layer, while popup background/selection theming stays deferred; the mask is therefore a true intersection of both render paths (finding 1). The v15 discriminant guard pins the byte encoding of CompletionPopup, the actual final pre-v16 variant, rather than the earlier LineNumbers variant (finding 2). The deterministic transactional bite now targets the production ordered-result helper: it consumes an iterator of Result<(String, Style)>, collects every result before taking the theme lock, and commits only the completed vector, so an Ok followed by an Err is both representable and guaranteed to leave the theme untouched (finding 3). An empty diagnostic child is named as an explicit reset to the built-in severity color, not as "unset" -- it blocks parent inheritance -- and acceptance covers a themed ui.diag parent plus an empty ui.diag.error child (finding 4). GPU acceptance now covers every distinct stage-1 route: modeline reverse, transient status text, minibuffer and isearch text, candidate-dropdown glyphs, normal/active search washes, and the existing gutter, selection, and diagnostic paths (finding 5). The prose and unset fixture use the exact ui-or-ui.* predicate (finding 6). Finally, the peer-selection acceptance drives the actual decoration collector with simultaneous local and peer selections and inspects their emitted colors; it is not a helper-only assertion (finding 7).

Revision 3 (framing round 2, findings 1–9): the cross-frontend contract is structural now — every face carries a stage-1 component mask, identical on both frontends and sized to what both can render today (the GPU gutter has no background layer; wash quads cannot recolor or reverse glyphs); out-of-mask components are ignored everywhere, so ui.selection = { fg = 1 } and ui.gutter = { bg = 1 } are component no-ops on the TUI too, and mask widening is a named, additive deferral (finding 1). Diag faces get a representable Default policy: Default fg means the built-in severity color, not "plain" — the minimap summary encodes diagnostic presence by copying that color into underline_color, where Default reads as "no mark", so an all-default diag face uses the built-in severity color rather than an unrepresentable plain mark (finding 2). The face predicate is explicit — name == "ui" || name.starts_with("ui.") — shared by the reservation, the counter-bump classification, and a merge-bare-ui acceptance case (finding 3). The consecutive-set bite interleaves render/observe between the mutations; two sets inside one dispatch legitimately coalesce into one emission (finding 4). Producer and gate caches advance on computation, not on emission: last_face_epoch is Option<u64> (the gate cannot short-circuit while the payload baseline is absent, guaranteeing the first authoritative send against an epoch-0 daemon), an identical rebuild records the epoch it inspected, and the summary inserts its new key even when payload equality withholds the message; Rust units pin single-recompute, which traffic assertions cannot see (finding 5). SearchView::new takes Option<ThemeHandle> — a bare core constructs an unthemed view, no contradiction (finding 6). ThemeFacts is appended after CompletionPopup, and a byte-level encoding pin of the final existing variant guards the placement — postcard discriminants are ordinal, and the new variant's own round-trip cannot detect a shift that would corrupt v15 peers (finding 7). The malformed-merge Lua acceptance pins only the order-independent user contract; the deterministic bite is a Rust unit on an ordered result stream, since Lua table iteration order is unspecified (finding 8). ui.selection themes the local selection only: the GPU splits its resolution path so peer selection rects keep the constant, and peer theming stays deferred with the peer-cursor palette (finding 9).

Revision 2 (framing round 1, findings 1–8): the theme mutation contract is transactional and monotonic — all four mutators parse and validate their full input before taking the lock, commit all-or-nothing, and bump from the prior counter value after every successful commit; set replaces the by_capture field, never the Theme value, so counters survive wholesale replacement (finding 1). The counter is split into syntax_epoch (keys the StyleGate) and face_epoch (keys the ThemeFacts producer), so a face-only edit never re-runs the tree-sitter span query; the minimap summary keys on both — diag faces feed its marks — and gains payload-equality suppression, so a non-diag face edit recomputes once per mutation and emits nothing (finding 8). Stage 2 takes protocol v17: once a v16 binary ships, a variant added under v16 would let two incompatible v16 schemas negotiate successfully (finding 2). Face application is unified as "a set face owns its surface" — both frontends replace the site default wholesale, with Default components meaning that frontend's plain rendering (GPU mapping table in Q#TH5); the finding-5 divergences ({ fg } keeping the GPU band bg, empty ui.selection diverging) are gone, and the residual divergences (Indexed palette meaning; GPU chrome honoring fg/bg/reverse only in stage 1) are named and tested. ThemeFacts is authoritative per attachment: the baseline seeds to None, every attachment receives exactly one table — empty included — after viewport declaration, so a frontend retaining face state across attachments is corrected even by an unthemed daemon (finding 4; the current GPU has no reconnect path, so this is contract, not accident). GPU ThemeFacts application invalidates the status-band shaping cache — E:/W: colors are baked into shaped rich text and re-shaping is gated on string equality, so a diag-face change with constant counts kept stale colors (finding 3). The grid views get a real theme path: EditorCore gains an injected ThemeHandle for ensure_search_overlay, and install_diag threads the handle to DiagnosticView; acceptance drives the dispatched-search and Lua diagnostic-attachment paths, not bare constructors (finding 6). The reserved namespace covers the bare root ui as well as ui.*, matching the inheritance walk's terminal (finding 7). Acceptance adds consecutive-set monotonicity, malformed-merge atomicity, GPU diag-recolor-with-constant-counts, owns-surface cross-frontend semantics, and absence assertions for face-only mutations.

Revision 1: initial framing.

Arc 4 ("Themes + extensibility surface", docs/roadmap-2026-07.md:83) names three deliverables: named UI faces wired to both frontends, a pmacs.gpu.set_font runtime font swap, and a Lua statusline-segment API. This framing covers stage 1 only — named UI faces plus the ThemeFacts wire channel (protocol v15→16). Font swap and statusline segments are stages 2 and 3, each with its own framing (Q#TH1). One branch (theme-faces), one PR.

Ground truth (as of `13dbadd`)

The theme substrate today

Theme { by_capture: HashMap<String, Style>, default_style: Style } — src/highlight.rs:59-67. One global instance behind ThemeHandle = Arc<Mutex<Theme>> (highlight.rs:190), owned by the SyntaxRegistry (src/syntax.rs:496, seeded Theme::default_dark() at :518, exposed via .theme() at :527; line refs re-verified after the #114/#115/#116 highlight-stack merges, whose bundled CUDA and shell grammars introduce no ui-named capture).
Theme::lookup (highlight.rs:161-172) tries the full dotted name, strips one .-segment at a time, and falls back to default_style — correct for syntax captures, wrong for faces (an unset face must mean "keep today's hardcoded look", which is not expressible as a Style on the semantic path).
Lua surface is complete and mounted: pmacs.theme.{set, merge, get, clear, default, current} — src/lua_bindings/mod.rs:6898-6993. set replaces by_capture wholesale but preserves default_style (:6913-6915). Style/color marshalling: lua_to_style :6865, lua_to_color :6780 (nil/"default" → Color::Default, 0..=255 → Indexed, {r,g,b} → Rgb).
Mutator shapes today: set parses the whole table into a scratch Theme before locking, then wholesale-replaces the locked value (:6906-6915) — already transactional, but the replacement would reset any naive counter carried on Theme. merge locks first and inserts while iterating (:6925-6931) — a malformed later entry errors out with earlier entries already applied.
Wire vocabulary already suffices: Color { Default, Rgb, Indexed } and Style { fg, bg, bold, italic, underline, reverse, underline_color } — pmacs-protocol/src/cell.rs:84-133. No alpha channel (relevant for GPU washes, Q#TH8).
Theme colors already cross the wire indirectly: scoped_style_spans (src/semantic_render.rs:1501-1566) clones the theme, resolves capture → Style, and ships StyleSpans. Nothing chrome-related crosses at all.

Chrome colors today — every one a hardcoded literal

Grid path (daemon paints cells for the TUI; paint_frame, src/editor.rs:2086, has &EditorState and therefore theme access):

Site	Where	Literal
Per-window mode line	`editor.rs:2474` (`paint_mode_line`)	`reverse: true` (`:2499-2502`)
Status/echo row	`editor.rs:2260` (`paint_status_line`)	`reverse: true` (`:2275-2286`)
Line-number gutter	`editor.rs:2320`	`fg: Indexed(8)` (`:2332-2335`)
Selection	`editor.rs:2375`	`cell.style.reverse = true` (`:2431`)
Minibuffer prompt/input/fill	`editor.rs:2541`	`Style::default()` (`:2571`, `:2588`, `:2613-2617`)
Minibuffer candidate suffix	`editor.rs:2605-2608`	`reverse: true`
Search prompt row	`editor.rs:2629`	`Style::default()` (`:2659`, `:2677`)
Search matches	`src/search.rs:362-378`	bg `Indexed(3)`/fg `Indexed(0)`; active bg `Indexed(11)`
Diagnostic severity color	`src/diag.rs:90-97`	`Indexed(1)/(3)/(6)/(8)` — shared by squiggle `underline_color`, column-0 marker, minimap mark

GPU path (frontend-local constants, pmacs-gpu/src/main.rs):

Site	Where	Literal
Status band bg	`:130`	`STATUS_BAND_BG [0.105, 0.105, 0.145, 1.0]`
Band left text (name/prompt)	`:4511`	`rgb(200,200,210)`
Band right readout	`:4496`	`rgb(168,168,180)`
Band `E:`/`W:` counters	`:3401`, `:3407`	`rgb(241,76,76)`, `rgb(245,245,67)`
Gutter digits	`:4534`	`rgb(120,120,135)`
Selection wash	`:6661`	`[0.31, 0.42, 0.82, 0.30]`
Search washes	`:6673-6674`	`[0.85,0.78,0.20,0.30]`, `[0.95,0.55,0.12,0.48]`
Diag squiggles/signs	`:6606-6623`	Error `[0.945,0.298,0.298]`, Warning `[0.961,0.961,0.263]`, Info `[0.231,0.557,0.918]`, Hint `[0.4,0.4,0.4]`
Surface clear / caret / menu / minimap	`:61-66`, `:73-74`, `:145-147`, `:111-114`	out of stage-1 scope (Deferred)

Indexed colors mean different things per frontend: the TUI defers to the user's terminal palette; the GPU has its own hardcoded xterm table (indexed_to_glyphon, main.rs:6552-6587). A face set with Indexed colors will render per-frontend, same as syntax styles do today — documented, not fixed here (Deferred).

The facts-channel template (LineNumbers, Q#UX1)

PROTOCOL_VERSION = 15 (pmacs-protocol/src/message.rs:1333); SUPPORTED_PROTOCOL_VERSIONS = [6..=15] (:1393). Standard bump shape: additive variant + daemon write-loop gate on negotiated_protocol_version (src/daemon.rs:1119-1121, :1153-1157); old peers receive nothing on the channel.
Producer pattern: cached-compare field on SemanticRenderState, emit-on-change from render_frame's emission list (src/semantic_render.rs:462-478; line_numbers_msg :810-825). Nothing emits before the frontend declares a viewport (:307-310).
Late join is free: per-session state is built fresh at attach (daemon.rs:1377-1381), and a baseline seeded to the frontend's default belief re-emits exactly the non-default state (semantic_render.rs:265-269). InlineAdornments additionally suppresses "nothing to say, nothing ever sent" (:297-304).
TUI drops the whole family silently (src/frontend.rs:380-422) — its chrome arrives pre-painted in the cell grid.
Pin tests updated every bump: assert_eq!(PROTOCOL_VERSION, …) at src/protocol.rs:1710, the resume-ladder test at :1774-1797 (accepted range and the rejected next version), and a postcard round-trip pin per new variant.
The dormant InstanceMessage::ModeLine(Vec<Cell>) (message.rs:506) is cell-shaped, unproduced, and not what this arc needs; it stays dormant.

Pre-existing staleness bug (this arc fixes it)

StyleGate (semantic_render.rs:226-246) keys the StyleSpans recompute on (parse-bundle Arc, CRDT generation, viewport) — never the theme. file_style_summary_msg similarly keys the minimap summary on (generation, diag_epoch) (:914). A mid-session pmacs.theme.set therefore re-ships nothing to a semantic frontend until the next buffer edit: the GPU keeps stale colors. The grid path is immune (SyntaxHighlightView clones the theme every render, highlight.rs:316), as is the ungated LSP-token span path. There is no theme mutation counter anywhere in src/. Q#TH6 introduces two (syntax/face) and folds them into the gates.

Decisions

Q#TH1 — Scope: stage 1 of Arc 4; faces + wire only

This PR delivers named UI faces resolved daemon-side, applied by both frontends, controlled through the existing pmacs.theme surface, and shipped to semantic frontends over a new v16 ThemeFacts channel. pmacs.gpu.set_font (stage 2) and the statusline-segment API (stage 3) are deferred with named hooks: stage 2 takes protocol v17 — once a v16 binary exists, adding another variant under v16 would let old and new v16 peers negotiate successfully despite incompatible schemas (postcard is not self-describing); reusing 16 is possible only if stage 2's wire shape lands in this same PR, which it does not. The segment API lands after faces so segments can carry face names instead of raw colors.

Q#TH2 — Faces are theme entries under the reserved `ui` / `ui.*` namespace

A face is an entry in the existing by_capture map whose name is exactly ui or starts with ui. -- no new type, no second map, no new Lua API. pmacs.theme.merge { ["ui.modeline"] = { bg = 236, fg = 252 } } works today, unmodified. The face predicate is one explicit function, used by every consumer — the docs reservation, Q#TH6's counter-bump classification, and the producer's key filter:

fn is_face_name(name: &str) -> bool {
    name == "ui" || name.starts_with("ui.")
}

The bare root ui is included because Q#TH4 makes it the walk's deliberate catch-all — a merge { ui = … } must bump face_epoch and emit ThemeFacts, not disappear into the syntax path. No tree-sitter capture or LSP token type is named ui or ui.* (verified against default_dark and the grammar queries). pmacs.theme.get("ui.x") keeps its existing lookup semantics (resolves through to default_style) — introspection tolerates that; rendering does not (Q#TH4).

Q#TH3 — Stage-1 face inventory: twelve faces

The roadmap's five surfaces, plus the two chrome families that already have daemon-side palettes (search, diagnostics), plus the minibuffer's one sub-face. Effects per frontend (unset = exactly today's literal, from the Ground-truth tables):

The mask column is the stage-1 component contract of Q#TH5: identical on both frontends, sized to what both can render today.

Face	Mask	Grid/TUI effect	GPU effect
`ui.modeline`	fg bg reverse	per-window mode-line row	status-band bg quad; band name + readout text
`ui.statusline`	fg	bottom status/echo row	echo-message segment text
`ui.minibuffer`	fg	prompt + input + fill; search prompt row	minibuffer/isearch band text
`ui.minibuffer.candidate`	fg	inline candidate suffix	minibuffer-dropdown candidate glyphs
`ui.gutter`	fg	line-number strip	gutter digit text
`ui.selection`	bg	local-region cells (wash)	local-selection wash RGB
`ui.search.match`	bg	lazy-match cells (wash)	match wash RGB
`ui.search.match.active`	bg	active-match cells (wash)	active wash RGB
`ui.diag.error`	fg†	severity color	squiggle + gutter sign + band `E:` counter
`ui.diag.warning`	fg†	severity color	squiggle + sign + `W:` counter
`ui.diag.info`	fg†	severity color	squiggle + sign
`ui.diag.hint`	fg†	severity color	squiggle + sign

† diag faces carry the special Default policy of Q#TH5: Default fg means the built-in severity color, not "plain".

The GPU status band is the mode-line analogue (one band, no separate echo row — a structural divergence this arc does not resolve), so it takes ui.modeline for its surface and ui.statusline/ui.minibuffer only for the text of the corresponding content it happens to be showing. ui.minibuffer.candidate colors the existing dropdown's candidate glyphs only; its background and selected-row quad remain popup chrome. Deliberately excluded from stage 1 (all named in Deferred): popup/menu/completion-dropdown backgrounds and selection quads, completion/menu glyph faces, ui.background, ui.caret, ui.modeline.inactive, minimap chrome, peer-cursor palette, inlay-hint face.

Q#TH4 — Resolution: `Theme::face()`, `None` when unset, never `default_style`

New method on Theme:

pub fn face(&self, name: &str) -> Option<Style>

Same dotted-prefix walk as lookup, but the walk returns None when nothing matches instead of falling back to default_style — an unset face must leave the paint site's hardcoded default untouched, and a user's pmacs.theme.default (a syntax fallback) must never bleed into chrome. The walk gives inheritance for free: ui.search.match.active falls back to ui.search.match, the four ui.diag.* to ui.diag, and everything to a deliberate catch-all ui (a theme can tint all chrome in one entry; a consequence of uniform walk semantics, not a special case). Callers pass full face names only.

Q#TH5 — A set face owns its surface, within its component mask

Wire Style cannot distinguish an omitted component from an explicitly-requested default, so per-component fallback to the site's old literal would diverge across frontends (ui.modeline = { fg = 252 } would drop the TUI's reverse video while the GPU kept its band background; an empty ui.selection would disable the TUI wash but leave the GPU wash intact). And an unmasked wholesale rule is not implementable either: the GPU gutter has only a foreground text layer (main.rs:4522), and the selection/search washes are background quads that can neither recolor nor reverse glyphs (main.rs:4801) — an unrestricted contract would make ui.selection = { fg = 1 } recolor TUI glyphs with no GPU counterpart. The unified rule:

Unset face (resolution None): the site's hardcoded default, both frontends, byte-identical to today.
Set face: the surface resets to plain, and the face's components within the face's mask (the Q#TH3 table) apply. Components outside the mask are ignored on BOTH frontends — the mask is the cross-frontend contract, sized to the intersection of what the two render paths can express today, so equivalence is structural rather than aspirational. ui.selection = { fg = 1 } is a component no-op on the TUI too (an effectively-empty wash face: wash disabled on both); ui.gutter = { bg = 1 } likewise renders as an all-default gutter face on both. Widening a mask later (GPU gutter background layer, wash glyph recolor/reverse, chrome bold/italic/underline) is additive and named in Deferred.
Default within the mask means that frontend's plain rendering, never "the old chrome look". On the TUI, plain = terminal defaults. On the GPU, a fixed mapping: Default fg ↦ the buffer-text default rgb(230,230,235) (main.rs:4482); Default bg ↦ the window background (an untinted band quad; no wash quad); reverse (in-mask only for ui.modeline) swaps fg/bg after the mapping. ui.modeline = { fg = 252 } therefore yields "plain background, color-252 text" on both frontends, and ui.selection = {} disables the selection wash on both — consistent, if deliberately drab; the user asked for an all-default surface.
Wash faces (ui.selection, ui.search.match, ui.search.match.active) remain a composition class: the masked face style (bg only, stage 1) replaces the default overlay argument of the existing merge_styles(cell, overlay) (src/overlay.rs:136 — non-Default components win, booleans OR), then merges over syntax-styled cells as today, so a wash never touches glyph fg in stage 1. The unset defaults remain the full overlay literals of today (Style { reverse: true, .. } for selection; the search literals as-is — the mask constrains face application, not the unset defaults). On the GPU the wash quad takes the face bg RGB with the site's current alpha — wire Style has no alpha; translucency is a rendering choice and stays frontend-local (Q#UX1 division).
ui.selection themes the local selection only. The GPU currently colors peer selection rects through the same DecorationKind::Selection helper (main.rs:4946); the implementation splits that resolution path — the local path resolves the face, the peer path keeps the constant — so peer rendering stays outside the theme system until the deferred peer-cursor palette arc. (The TUI peer path, overlay_paint.rs, is already separate.)
ui.minibuffer.candidate has one GPU effect in stage 1: its masked fg is the default_color of the existing minibuffer dropdown candidate TextArea (main.rs:4594-4610). This does not theme the popup background or selected-row quad; those remain on their current constants and in Deferred. On the grid path the same face colors the inline selected-candidate suffix.
Diag faces: the fg component is the canonical severity color (the diag.rs:84-97 contract: squiggle underline_color, marker, minimap mark all share it), with a face-family-specific Default policy: Default fg means the built-in severity color, not plain. The severity color doubles as the presence encoding in the minimap summary — scoped_file_summary copies it into the line's underline_color (semantic_render.rs:1779), and the GPU reads underline_color == Default as "no diagnostic mark" (main.rs:5551) — so a plain severity color is unrepresentable and ui.diag.error = {} explicitly resets that child to the built-in error color on every surface (squiggle, sign, minimap, band counter). It is not absent: an exact empty child stops Q#TH4's walk, so it overrides an inherited ui.diag color with the built-in. Scope of "built-in" (round 1 finding 4): a SET face with a concrete color unifies all surfaces on both frontends, but the per-surface built-in DEFAULTS keep their pre-existing values — the TUI and the wire summary use Indexed(1/3/6/8), while the GPU's squiggle, sign, and counter constants are historical bright RGBs that differ from the minimap's converted Indexed marks. That divergence predates this arc and stays, because unset faces must render byte-identically to before.

Residual divergence, accepted and tested: Indexed colors mean the user's terminal palette on the TUI and the indexed_to_glyphon table on the GPU (pre-existing; identical to syntax styles today).

Q#TH6 — Two monotonic mutation counters; transactional mutators

Theme gains syntax_epoch: u64 and face_epoch: u64 (both 0 at construction), owned by the same mutex. The mutation contract for the four Lua bindings — the only mid-session mutation paths:

Parse before locking. The production set/merge transaction helper accepts a commit mode plus an ordered iterator of mlua::Result<(String, Style)>, collects the whole iterator into mlua::Result<Vec<(String, Style)>>, and only after Ok(Vec) acquires the theme mutex and commits in the requested mode. The Lua table iterator maps each raw (name, style_table) entry through lua_to_style into that result stream — whose own lookups PROPAGATE errors (round 1 finding 2): Table::get runs __index, so a raising metatable fails the transaction rather than silently parsing as an all-default style; boolean fields keep Lua truthiness by design. default parses its one Style before locking; clear has no input to parse. set already parses into a scratch value pre-lock; merge today inserts while iterating under the lock (mod.rs:6925-6931), so a malformed later entry currently leaves earlier entries applied — that shape is disallowed.
Commit all-or-nothing. Every entry applies, or the binding errors with the theme untouched (and therefore no counter bump and no downstream emission).
Bump from the prior value after every successful commit. set replaces the by_capture field — never *theme = new_theme, whose zeroed counters would let consecutive set calls share an epoch and stay invisible to every gate — then bumps; counters only ever increment. Per mutator: set and clear bump both counters; merge classifies every committed key through is_face_name (Q#TH2 — bare ui is a face key) and bumps syntax_epoch iff any non-face key committed, face_epoch iff any face key did; default bumps syntax_epoch only.

Consumers:

StyleGate gains a syntax_epoch field, compared in matches() — a capture recolor forces the tree-sitter span recompute and the changed spans ship (the fix for the pre-existing GPU staleness bug, bite-able on its own: mid-session pmacs.theme.set with no buffer edit must produce a StyleSpans re-emission). A face-only edit leaves syntax_epoch untouched and never re-runs the query.
file_style_summary_msg's cache key becomes (generation, diag_epoch, syntax_epoch, face_epoch) — face_epoch belongs in the key because ui.diag.* feeds the minimap marks — plus a payload-equality suppression: a face edit that leaves the summary unchanged (e.g. ui.modeline) recomputes it once per mutation, not per tick, and emits nothing. The cache key advances on computation, not on emission — the suppressed send still inserts the new key, or the recompute repeats every tick and the performance contract is a fiction. Rust units pin the single-recompute (by asserting the advanced cache state); traffic assertions cannot see repeated computation.
The ThemeFacts producer gates on face_epoch (Q#TH7).

The LSP-token span path and the whole grid path already re-resolve per tick/frame and need nothing.

Q#TH7 — `ThemeFacts` channel: bufferless resolved-face table, protocol v15→16

/// Themes arc (Q#TH7, protocol v16). The daemon-resolved UI faces.
/// The theme is one global instance, so this is bufferless (the
/// `MinibufferPrompt` shape). Complete replacement each send: a
/// face absent from `faces` is unset, and the frontend uses its
/// own default for that surface. Cached-compare suppressed;
/// daemon-gated `>= 16`.
ThemeFacts {
    /// Every stage-1 face that resolves to a style (Q#TH4 walk),
    /// full names, sorted by name for deterministic comparison.
    faces: Vec<ThemeFace>,
},

pub struct ThemeFace {
    pub name: String,
    pub style: crate::cell::Style,
}

Resolution is daemon-side: the producer walks the known face list (the Q#TH3 twelve) through Theme::face() and ships concrete entries — frontends do exact-name lookup, no walk, no inheritance logic. The daemon owns face semantics; frontends own pixels (Q#UX1). No epoch on the wire — the payload is self-contained and the house facts style carries no counters.
The producer is peer-version-aware (round 1 finding 3): daemon sessions construct via SemanticRenderState::for_peer, and below v16 no ThemeFacts is produced at all — more importantly, no ui.diag.* face is folded into the FileStyleSummary marks, because that summary is an ungated pre-v16 channel and a v15 peer must not receive face-derived minimap colors while its squiggles, signs, and counters stay unthemed. The write-loop gate remains as the belt-and-braces filter. The summary cache key zeroes its face-epoch component for such peers (no whole-file recompute per face edit that could never change their marks).
Producer: theme_facts_msg on SemanticRenderState, called from the render_frame emission list. Per-tick cheapness comes from a last_face_epoch: Option<u64> gate seeded None — Option, not a bare zero, because an unthemed daemon sits at face_epoch == 0 and a 0 == 0 short-circuit would starve the first authoritative send; the gate can only short-circuit once it has recorded an inspected epoch. Emission truth comes from comparing the rebuilt table against last_theme_faces, also seeded None. Both records advance on computation: an identical rebuild (e.g. after a payload-equal re-merge) records the epoch it inspected even though nothing ships, so subsequent ticks skip — a Rust unit pins the no-rebuild second tick. Every attachment receives exactly one authoritative table — the empty table included — with its first emission after viewport declaration, cached-compare suppressed thereafter. One small message per unthemed session buys a reconnect-safe contract: a frontend that retains face state across attachments is corrected even by an unthemed daemon, instead of depending on every frontend starting empty. (The current GPU has no reconnect path — a disconnect only swaps the displayed text, main.rs:1435 — so this is contract, not a load-bearing assumption about today's client.)
Variant placement: ThemeFacts is appended after CompletionPopup (message.rs:961), the current final InstanceMessage variant. Postcard discriminants are ordinal — a variant inserted earlier shifts every later variant's tag and silently corrupts v15 peers on channels that are not gated, and the new variant's own round-trip test cannot detect the shift. A byte-level encoding pin of CompletionPopup -- the final existing variant, so any insertion before any v15 variant moves its ordinal -- asserts its serialized bytes, discriminant included, are unchanged by the v16 build.
Gating: PROTOCOL_VERSION 15→16 with a ladder paragraph; SUPPORTED_PROTOCOL_VERSIONS grows 16; daemon write-loop peer_knows_theme_facts = negotiated_protocol_version >= 16 + skip arm; TUI silent-drop arm (frontend.rs:380-422); GPU debug-name arm (main.rs:5606-5628); ThemeFace re-exported from pmacs-protocol/src/lib.rs; pin tests at protocol.rs:1710 and the ladder test (accept 16, reject 17); postcard round-trip pin.
docs/semantic-frontend-protocol.md gains the channel's contract section.

Q#TH8 — GPU application: exact-name map, Q#TH5 mapping, shaping-cache invalidation

State gains faces: HashMap<String, Style>; the apply_attach_message arm replaces the map, invalidates the status-band shaping cache, and request_redraw()s (extending the LineNumbers arm shape, main.rs:2686-2692). The invalidation is load-bearing, not belt-and-braces: the E:/W: counter colors are baked into glyphon rich-text attributes at compose time (compose_status_spans, main.rs:3390-3441), and refresh_status_line skips re-shaping whenever the composed strings are unchanged (main.rs:3502-3546) — without clearing those cached comparison strings, a diag-face change with constant counts keeps stale counter colors indefinitely.

A newly accepted FileStyleSummary drops the cached minimap vertices (round 1 finding 1): theme recolors and diagnostic republishes ship a new summary at an UNCHANGED generation, and the minimap cache keys only on (generation, dims, scroll) — without the explicit invalidation the stale strokes survive until an edit, resize, or scroll. The daemon payload-suppresses identical summaries, so every accepted one is genuinely new.

Each themed site resolves per draw with the Q#TH5 rule: face absent → today's site constant; face present → the face's in-mask components, with Default fg ↦ the buffer-text default, Default bg ↦ the window background (untinted quad / no wash quad), reverse (ui.modeline only) as a post-map swap, and the diag Default-fg ↦ built-in-severity-color policy. Out-of-mask components are never read. Rgb maps directly; Indexed through the existing indexed_to_glyphon table; quad colors convert u8 RGB into the same color space the current float constants use; band/wash alphas keep their current values. Peer selection rects resolve through the split constant path, never the face (Q#TH5). The minibuffer candidate face supplies the existing dropdown TextArea.default_color; refresh_mb_buffer already runs before each dropdown paint (main.rs:4337-4341), and the default color is resolved again when preparing the TextArea, so no new shaping-cache contract is needed for its fg-only mask.

Q#TH9 — Grid application: one theme clone per frame; views gain the handle

paint_frame clones the Theme once per frame (single mutex lock, same discipline as SyntaxHighlightView::render) and passes &Theme down to paint_mode_line / paint_status_line / paint_minibuffer / paint_search_prompt / paint_line_number_gutter / paint_local_selection (signature additions; paint_mode_line takes the resolved Style since it is a pure formatter). SearchView and DiagnosticView gain a ThemeHandle constructor parameter and resolve faces under the lock per render — the exact SyntaxHighlightView::new precedent (highlight.rs:246).

Ownership, named: SearchView is constructed inside EditorCore::ensure_search_overlay (src/editor_core.rs:858), and EditorCore owns no syntax state — so EditorCore gains a theme: Option<ThemeHandle> field, injected once at editor bring-up right after SyntaxRegistry construction, and SearchView::new(store, theme: Option<ThemeHandle>) takes the Option directly: ensure_search_overlay passes the field through unconditionally, so a bare core (unit-test construction, field None) still constructs a working view that resolves no faces and paints today's literals — no contradiction between "views take the handle" and "bare cores have none". DiagnosticView is attached by the Lua path — install_diag (src/lua_bindings/diag.rs:46, construction at :220) — which gains the handle as a parameter, threaded from the installer call site (mod.rs:8626). Acceptance exercises the real attachment paths: a dispatched C-s reaching ensure_search_overlay, and the Lua diagnostic attachment — never bare constructors. The completion popup and menu keep their literals (faces deferred).

Q#TH10 — `pmacs.theme.set` wholesale semantics include faces

set replaces the whole by_capture map today and therefore wipes faces along with captures; merge is the incremental path. This is kept unchanged — a "theme" legitimately includes its chrome, and a theme-switching user wants no stale faces from the previous theme. Documented in the Lua API docs alongside the ui. namespace reservation.

Bets

The reserved-namespace design (Q#TH2) means zero new Lua API and zero protocol vocabulary beyond one variant — the whole feature rides existing Style plumbing.
The authoritative-per-attachment contract (seed None) makes late-join and stateful reconnect correct by construction for the price of one small message per session; unthemed steady-state traffic remains zero.
Daemon-side resolution keeps both frontends walk-free and makes face inheritance testable in one place.
The split-counter fix (Q#TH6) closes the mid-session staleness bug at one-u64-compare per-tick cost, while face-only edits stay off the tree-sitter path entirely; the one whole-file summary recompute per face mutation is user-action-rate, not tick-rate.
The owns-surface-within-mask rule (Q#TH5) is the only semantic expressible with the existing Style (no omitted-vs-default distinction) that renders equivalently on both frontends, and the masks make that equivalence structural — the contract promises only what both render paths can draw today, and widening a mask later is additive. Its cost — partial faces reset the rest of their surface to plain, and some components are simply not themable yet — is documented and falls only on users who theme.
Unset faces reproduce today's rendering byte-identically on both frontends — the acceptance baseline tests pin this, so shipping stage 1 changes nothing for users who theme nothing.
Twelve faces cover the roadmap's named surfaces; the deferred chrome (popups, background, caret) reuses the same substrate without another protocol bump.

Deferred (named)

Popup/menu/completion-dropdown background, selected-row, and general glyph faces (ui.popup, ui.menu, …; the fg-only ui.minibuffer.candidate exception is in scope); ui.background and ui.caret (GPU-only effect; background interacts with the TUI's terminal-default philosophy and deserves its own decision); ui.modeline.inactive (active/inactive split); minimap chrome faces; peer-cursor palette theming (overlay_color.rs — deliberately not on the wire today); inlay-hint face (ui.inlay_hint — semantic_render.rs:1137 names the gap; its adornment producer needs the same epoch treatment when it lands); alpha on the wire (washes keep frontend-local alpha until a real theme needs to change it); unifying Indexed palette meaning across frontends; named-theme registry / light-theme builtin / persistence (no unified config surface yet — handoff §6); the grid-vs-wire default_style asymmetry (uncaptured text: wire ships nothing where the grid paints the base style — orthogonal to faces); mask widening (GPU gutter background layer; wash glyph recolor/reverse; a distinct GPU echo surface so ui.statusline could carry bg; chrome bold/italic/underline — attribute re-shaping that compounds the Q#TH8 shaping-cache invalidation); ui.selection for peer selections (rides the deferred peer-cursor palette; the GPU resolution path is already split); pmacs.gpu.set_font (stage 2, protocol v17 per finding 2 — and the pmacs-gpu-design.md:299 claim that font customization needs no wire change is superseded by the Q#UX1 lesson, to be corrected in that framing); Lua statusline-segment API (stage 3 — should ship segments carrying face names, hence after this arc).

Acceptance

Suites: tests/theme_faces_acceptance.rs (grid-path rendering + Lua surface + wire facts) and the existing pin/round-trip homes (src/protocol.rs); GPU behavior in pmacs-gpu behind PMACS_REQUIRE_GPU=1 (frame-difference pattern, main.rs:7877+). Keybinding-driven tests dispatch keys, never pmacs.command.invoke.

Unset = today, byte-identical: with neither a bare ui entry nor any ui.* entry, a painted frame (mode line, status row, gutter, minibuffer, selection, search matches, diag squiggle) is cell-for-cell identical to the pre-arc rendering; additionally a loud pmacs.theme.default (syntax fallback) leaks into no chrome cell (pins Q#TH4's None-not-default_style).
Each surface face applies (grid): setting ui.modeline, ui.statusline, ui.minibuffer, ui.minibuffer.candidate, ui.gutter each changes exactly its rows'/strip's cells to the masked face style on the next frame, per-cell asserted.
Owns-surface semantics (Q#TH5): ui.modeline = { fg = 252 } paints the grid mode line with fg 252 and no reverse video (partial face resets the surface to plain); ui.selection = {} leaves selected cells identical to unselected ones.
Mask enforcement (round 2 finding 1): ui.selection = { fg = 1, reverse = true, bg = B } renders exactly as { bg = B } on both frontends — grid per-cell (glyph fg untouched under the wash), GPU frame identical to the bg-only variant; ui.gutter = { bg = 1, reverse = true, fg = F } renders exactly as { fg = F } on both.
Wash faces merge: ui.selection and both search faces compose over syntax-styled cells with merge_styles semantics — a bg-only wash keeps the syntax fg under the wash (per-cell fg+bg assertions, not any-styled-cell). Search asserted through a dispatched C-s reaching ensure_search_overlay (the real construction path), never a bare constructor.
Diag faces: ui.diag.warning recolors the squiggle underline_color, the column-0 marker, and the minimap mark, attached via the real Lua diagnostic path (install_diag); unset severities keep Indexed defaults. Empty diag face (round 2 finding 2, clarified in round 3): with no parent, ui.diag.error = {} renders identically to the built-in error face on every surface -- squiggle, sign, minimap mark (present, not vanished), band counter. With ui.diag = { fg = C } also set, the exact empty ui.diag.error child blocks inheritance and resets errors to the built-in color while warning/info/hint remain C.
Inheritance: with only ui.diag set, all four severities resolve to it; an explicit ui.diag.error then wins for errors only. Same for ui.search.match.active ← ui.search.match.
Bare ui is a face (round 2 finding 3): pmacs.theme.merge { ui = … } bumps face_epoch and ships a ThemeFacts table with every stage-1 face resolved to the catch-all, with no StyleSpans re-emission (the key classifies as face, not syntax).
Mid-session recolor, no edit (the staleness bite): a semantic session with a grammar-backed buffer receives fresh StyleSpans after pmacs.theme.set changes a capture color with zero buffer edits — fails against pre-arc StyleGate. Twin for the minimap: FileStyleSummary re-emits on a diag-face change.
Consecutive set monotonicity (round 1 finding 1, observation shape per round 2 finding 4): set → render/observe one StyleSpans emission → set (different capture colors) → render/observe a second emission — fails if wholesale replacement resets the counters and the second set shares the first's epoch. Two mutations inside one dispatch legitimately coalesce: a companion assertion pins that back-to-back sets followed by one render yield one emission.
Malformed merge is atomic: the Lua acceptance pins the order-independent user contract — one pmacs.theme.merge carrying a valid and a malformed entry errors, every entry of that merge is absent afterwards, and no ThemeFacts or StyleSpans re-emission occurs. Lua table iteration order is unspecified (round 2 finding 8), so the deterministic bite drives the production transaction helper with an ordered iterator [Ok((valid_name, valid_style)), Err(malformed)]. The helper must return the error before acquiring the theme lock; the unit asserts the pre-existing map, syntax_epoch, and face_epoch are all unchanged. An implementation that locks and inserts while consuming the iterator fails deterministically.
ThemeFacts emission discipline: every v16 semantic attachment receives exactly one authoritative table after viewport declaration — the empty table for an unthemed session (face_epoch still 0; pins the Option gate of Q#TH7) — then silence; after pmacs.theme.merge of a face, exactly one message with the resolved sorted table; an identical re-merge emits nothing; pmacs.theme.clear emits the empty table.
Face-only mutations stay cheap (round 1 finding 8): after a ui.modeline merge, no StyleSpans and no FileStyleSummary re-emission occurs (absence assertions) while ThemeFacts ships.
Caches advance on computation (round 2 finding 5, Rust units): after an identical re-merge, theme_facts_msg rebuilds once and the next tick skips via the recorded epoch; after a non-diag face mutation, the summary recomputes once and its cache key advances despite the suppressed emission — asserted on the internal cache state, since traffic cannot show repeated computation.
Resolution is daemon-side: with only ui.diag set, the shipped table contains the four concrete ui.diag.* entries (frontends never walk).
Late join: faces set via init.lua/first session; a second semantic frontend attaching later receives the face table among its first frames without any mutation occurring post-attach.
Version gate and placement: a v15 peer session never receives ThemeFacts (daemon skip arm); pin tests updated — assert_eq!(PROTOCOL_VERSION, 16), ladder accepts 6..=16 and rejects 17, ThemeFacts postcard round-trip pin, and a byte-level encoding pin of CompletionPopup, the final v15 variant, proving the appended placement shifted no existing discriminant (round 2 finding 7, corrected in round 3).
TUI drop arm: grid-session frontend consumes a ThemeFacts message without error (silent drop, family test pattern).
set wipes faces (Q#TH10): pmacs.theme.set with a captures-only table removes prior faces — next frame chrome is back to defaults and ThemeFacts ships the empty table.
GPU surface/text routes (PMACS_REQUIRE_GPU=1): an empty ThemeFacts table renders identically to never-themed. A ui.modeline bg changes the band, and a modeline face with reverse = true swaps the sampled band/text colors after Default mapping. A ui.gutter fg changes only the gutter digits. With the composed strings held constant, ui.statusline recolors a transient-message left segment, while ui.minibuffer recolors both a live minibuffer and an isearch band without recoloring the ordinary buffer-name state. ui.minibuffer.candidate recolors the actual dropdown candidate glyph region while leaving its popup background and selected-row quad at their constants.
GPU wash routes (PMACS_REQUIRE_GPU=1): a local selection uses ui.selection (including the mask-equivalence assertion in item 4); simultaneous normal and active search decorations use ui.search.match and ui.search.match.active respectively, with distinct sampled/decoded quad colors and unchanged glyph fg.
GPU diagnostic route and shaping invalidation (PMACS_REQUIRE_GPU=1): changing ui.diag.error while the composed band text and diagnostic counts stay constant changes the squiggle, gutter sign, minimap mark, and E: counter. The counter assertion fails without clearing the rich-text comparison cache; the empty-child reset case is item 6.
Peer selections keep the constant (round 2 finding 9, integration shape corrected in round 3): construct simultaneous, non-overlapping local and peer selections and drive the actual decoration_background_vertex_bytes / collect_peer_rects path. Decode the emitted vertex colors: the local rectangle uses ui.selection, while the peer rectangle remains the hardcoded constant. A helper-only resolver assertion is insufficient.
Lua surface unchanged: pmacs.theme.current() lists both bare ui and ui.* entries alongside captures; get("ui.modeline") returns the set style (existing lookup semantics).
Raising __index is transactional (PR round 1 finding 2): a merge whose style value carries a raising __index metatable errors with the metatable's own message, commits nothing — including its valid sibling — and emits nothing.
v15 peers get no face-derived summary marks (PR round 1 finding 3): with a diag face set, a for_peer(…, 15) producer ships summary marks at the built-in severity color and produces no ThemeFacts; the for_peer(…, 16) twin resolves the face.
Same-generation summary updates repaint the GPU minimap (PR round 1 finding 1, PMACS_REQUIRE_GPU=1): two summaries at one generation with different mark colors render different frames — fails without the cache invalidation on accept.

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