pmacs/docs/in-buffer-completion-framing.md

In-buffer completion popup — framing (Arc 1a)

pmacs has a complete completion system that nothing drives. M4.7 shipped the LSP completion store + CompletionView popup (src/completion.rs); M4.11 shipped the provider framework — registry, scoring, dedup, and four providers (lsp=100, snippets=80, project_symbols=60, dabbrev=20 by priority; src/completion_framework.rs); the async LSP request path (LspManager::request_completion, src/lsp.rs:1665) works and is exercised by m4 acceptance tests. But there is no keybinding, no typed-char trigger, CompletionView is never instantiated, and no GPU wire message exists. This arc wires it end-to-end in both frontends: type, see candidates, TAB/RET accept.

Roadmap context: docs/roadmap-2026-07.md Arc 1a. Closest wire precedent: docs/gpu-minibuffer-framing.md (the SearchPrompt/MenuPrompt/MinibufferPrompt family). Tightened 2026-07-07 after a code review pass against the current tree (findings folded into Q#C1/C3/C6/C7/C8/C9 below).

What already exists (verified)

• Framework: CompletionRegistry::collect(ctx) is synchronous — filters enabled providers by priority, scores against ctx.prefix (exact=1000 / prefix=600 / word-boundary=300 / substring=100), dedups by (label, insert_text), sorts (completion_framework.rs:292-333). Rc<RefCell<…>> — main-thread only. Instantiated at startup (editor.rs:243) and exposed as pmacs.completion.{register,collect, context_for,snippets.*} — never called by builtin Lua.
• The LSP provider does not request, and is globally scoped — it drains every cached (server_id, uri) entry in the store, ignoring context (completion_framework.rs:617-645), so unmodified it can surface stale candidates from other buffers/servers. Fresh requests are the editor's job: pmacs.lsp._request_completion_raw → awaitable handle (builtin/runtime/lsp.lua:585-597), response absorbed into the store with positions already normalized to bytes (lsp.rs:2630-2647).
• collect does not filter non-matches — score_match returns −1 for a candidate that misses the prefix, but collect keeps it and merely sorts it last (completion_framework.rs:292-333); a no-hit prefix would still yield a popup full of unrelated rows.
• The public attachment accessor does not flush — interactive LSP commands resolve via the local attached_for_active(), which runs flush_did_change first so the server answers against current text (builtin/runtime/lsp.lua:520-533); the public pmacs.lsp.active_attachment() is deliberately side-effect-free and skips the flush (lsp.lua:541-545).
• buffer.after-edit carries no payload — both edit paths fire it with empty args (editor.rs:575, daemon.rs:1923); a driver cannot see what changed, only that something did.
• Trigger characters: CompletionTriggers::from_capabilities + should_fire(ch) per server (completion.rs:406-454), Lua-exposed. No prefix-extraction helper exists anywhere — the driver must derive the word before the cursor itself.
• CompletionView is a cell-owning popup (kind glyph + label + detail, reverse-video selection, width ≤ 40, CJK-aware) — but it reads the raw LSP store, not framework candidates, and the TUI overlay loop hands every overlay the full window viewport (editor.rs:1667-1669); nothing positions a sub-rect popup today. MenuView is the precedent for a self-positioning cell popup.
• Dispatcher shadows already exist for minibuffer (editor.rs:520), menu (:500), isearch (:511).

Decisions

Q#C1 — The driver is builtin Lua, core stays a library

A new builtin/runtime/completion.lua: derives the prefix (word chars [A-Za-z0-9_] before the cursor), decides when to open (Q#C9), fires the LSP request through a flushing accessor (Q#C8), runs pmacs.completion.collect, filters to score >= 0 (collect returns non-matches sorted last; Lua receives score, so the driver drops them — a Rust-side filter inside collect would change M4.11 semantics/tests and is left as a follow-up), and publishes the session (Q#C2) only when at least one row survives. Mirrors how lsp.lua drives every other LSP surface. Refresh-on-typing rides the same after-edit hook while the session is open; the session closes when the prefix dies (Q#C3's validation, C-g, or an edit that kills the word). Nit rolled into phase 1: pmacs.completion.context_for cannot express a Char trigger (lua_bindings/mod.rs:9964 maps only incomplete-vs-invoked) — either extend it or have the driver pass raw ctx tables (already supported).

Q#C2 — Core-owned session state, the search-store pattern

A frontend-agnostic CompletionPopup session on EditorCore (like menu: SharedMenu): {buffer_id, anchor_byte, prefix_len, candidates, selected, total}. Lua publishes into it; both frontends render from it; keys resolve against it daemon-side. Control is daemon-owned even though rendering is frontend-local — the Q#UX1 lesson, applied from day one this time. Candidates carry {label, kind, detail, insert_text} (framework CompletionCandidate projected down).

Q#C3 — Key capture: a partial dispatcher shadow, not buffer-local binds

While the session is open, dispatch_key routes only TAB / RET / C-n / C-p / Up / Down / ESC / C-g to dispatch_completion_key (accept / accept / next / prev / next / prev / close / close); everything else falls through to normal dispatch, so printable keys keep self-inserting and motion keys work. This is the fourth member of the existing shadow family and avoids the bind/unbind lifecycle discipline that transient buffer-local keymaps would need. Considered and rejected: minibuffer-style full shadow (typing must insert); add_intercept (sees edits only, never nav chords); buffer-local binds (workable — the *buffer-list* idiom — but the teardown hazard buys nothing here).

Session validity is enforced in core, post-dispatch — not by hooks. Cursor motion fires no hook (buffer.after-edit is edits-only, editor.rs:573), so "close when the cursor leaves the word" cannot be Lua-driven. After any dispatched action while the session is open, the dispatcher runs a validation step: the session survives only if the active buffer still matches buffer_id, the cursor sits inside [anchor .. anchor + current-word-end], and the prefix re-derived from the buffer still starts at anchor. Anything else — motion off the word, buffer switch, window change, undo that rewrote the region — closes the session. This also covers remote/CRDT edits landing under the popup: the next dispatch (or the producer tick) revalidates against the shifted text.

Q#C4 — TUI popup: rework CompletionView on the MenuView pattern

CompletionView switches its data source to the Q#C2 session and becomes self-positioning like MenuView: compute its own sub-rect anchored to the row below the cursor (above when near the window bottom), clamped to the window and offset past the gutter (viewport.gutter_w), painting ≤ POPUP_VISIBLE rows. Attached once per window like MenuView, self-suppressing when the session is closed or belongs to another buffer.

Q#C5 — Wire: InstanceMessage::CompletionPopup, protocol v15

Additive over v14; SUPPORTED = [6..15], daemon-gated >= 15, produced by semantic_render::completion_popup_msg with the family's cached-compare suppression:

InstanceMessage::CompletionPopup {
    buffer_id: BufferId,
    anchor: Option<u64>,        // byte offset of the prefix start; None = closed
    prefix_len: u32,            // bytes of typed prefix (frontend may embolden)
    rows: Vec<CompletionRow>,   // windowed slice (≤ POPUP_VISIBLE = 10)
    selected: Option<u32>,      // within `rows`
    total: u32,
}
CompletionRow { label: String, kind: u8, detail: Option<String> }

Byte anchor, not pixels — the GPU already maps byte→glyph rect for the caret and presence washes; first byte-anchored popup on the wire (menu anchors at the click pixel locally). Rows are display-only; accept is a daemon round-trip, so insert_text never ships.

Q#C6 — GPU input while the popup is open: an explicit key predicate

The existing gates are all-or-nothing (daemon_intercepts_keys, pmacs-gpu/src/main.rs:1913; dispatch_idle) — reusing them would round-trip typing too, killing optimistic latency exactly when the user is mid-word. Instead the GPU gets an explicit is_completion_control_key(key, mods) predicate, checked before the optimistic-insert path and before local key handling, active only while CompletionLocal.is_some(): exactly TAB / RET / ESC / C-g / C-n / C-p / Up / Down forward as FrontendEvent::Key round-trips into dispatch_completion_key; every other key stays on its normal path (plain chars optimistic, chords per the usual forwarding rules). Three keys need the gate specifically because their default handling is wrong under a popup: RET and TAB are optimistic-eligible today (they reduce to plain inserts, main.rs:5300-area), and ESC is a hardcoded local exception (main.rs:1423) that would be swallowed and never reach the daemon — it must be conditionally forwarded while the popup is open. Rendering: a CompletionLocal mirror + a dropdown layer cloned from the mb_dropdown_* functions, anchored at the anchor byte's glyph rect instead of the status band, clamped to the window (the F-007 fit logic).

Q#C7 — Accept semantics: validate, then replace

Accept re-validates before touching the buffer: the active buffer, cursor, anchor, and the prefix currently in the text must all still match the session (the Q#C3 invariant, re-checked at the moment of accept — a remote edit or race can invalidate between frames). On mismatch, accept is a no-op that closes the session. On match, it replaces [anchor .. cursor] with the candidate's effective_insert_text() through the normal command/edit layer (one undo entry; fires buffer.after-edit, so LSP didChange and styling refresh ride existing machinery), then closes the session. Snippet bodies insert literally in v1 — no tabstop engine (deferred).

Q#C8 — LSP scoping + freshness: flush first, scope to the attachment

Two correctness rules, then the UX:

• Flush before requesting. didChange is debounced; a request issued without flushing answers against stale text. The driver must not use the non-flushing pmacs.lsp.active_attachment() — lsp.lua grows a public flushing accessor (wrapping the local attached_for_active(), lsp.lua:520-533) that the driver calls before request_completion, exactly as every interactive LSP command already does internally.
• Scope candidates to the attachment. The built-in LSP provider drains the whole store across all (server, uri) keys. Fix in the framework: CompletionContext gains uri: Option<String> (the driver fills it from the attachment record) and the provider reads only that URI's entries. Fallback if the context change proves awkward: disable the built-in LSP provider for the driver path and have Lua merge pmacs.completion.items(rec.server, rec.uri) itself — either way, no cross-buffer candidates.

UX: publish immediately from the synchronous providers (dabbrev/snippets/project-symbols feel instant), fire the LSP request, and re-collect + re-publish when the response lands (handle:on_complete). isIncomplete responses re-request on further typing. No spinner; the popup just gets better a beat later.

Q#C9 — Trigger policy without edit metadata

buffer.after-edit fires with no payload from both edit paths (editor.rs:575, daemon.rs:1923), so the driver cannot see what changed — it must reconstruct intent from state. Policy (v1):

• The driver keeps a per-invocation snapshot {buffer, revision, cursor}.
• Open on after-edit only when: the active buffer is unchanged, the cursor sits at the end of a word with prefix ≥ 2, and the cursor advanced by exactly one codepoint since the last snapshot (the single-char-typing signature) — or the char before the cursor is a server trigger character (should_fire).
• Paste, undo/redo, kill, and remote edits never auto-open (their cursor delta ≠ 1 or the region signature doesn't match); C-M-i covers the deliberate cases.
• While open, any after-edit re-derives the prefix from the buffer and refreshes or closes — no metadata needed, the text is the truth.

Named alternative, deliberately not taken now: giving buffer.after-edit an edit payload (buffer id, kind, range). Variadic Lua handlers would tolerate the new args, but the PR #52 revert history says hook-signature changes must not ride along in a feature bundle — if the heuristic proves flaky, the payload becomes its own small, separately-validated PR.

Phasing (each phase independently green + user-validated)

1. Core + TUI, no wire change. Session store + dispatcher shadow with post-dispatch validation (Q#C3) + CompletionView rework + builtin/runtime/completion.lua driver (Q#C1/C9 policy, score ≥ 0 filter) + validated accept (Q#C7) + completion.at-point — plus the small Rust/Lua seams the review surfaced: CompletionContext.uri + LSP-provider scoping, the flushing attachment accessor, and the context_for char-trigger fix (Q#C8/C1). Validate in the standalone TUI and a TUI-attached daemon.
2. Wire + GPU. Protocol v15, producer + daemon gate, GPU CompletionLocal + dropdown layer + the RET/TAB optimistic gate.
3. Polish + docs. isIncomplete re-query, per-server trigger-chars, as-built notes folded into this doc.

Arc 2 interleave points: after phase 1 and after phase 2 (query-replace and kill-ring are the named next table-stakes items).

Categorical bets (score at close)

1. The prompt-family pattern generalizes a fourth time — producer / cached-compare / gate / local-mirror drop in without core surgery. Risk concentrates in the one new element: byte-anchored positioning.
2. Synchronous collect is fast enough per keystroke. dabbrev scans the whole buffer text per call — O(buffer) on every refresh. Bet: fine at typical file sizes; a cap/debounce is the fallback, not a redesign.
3. RET/TAB/ESC routing — some path will both insert and accept (or neither), or ESC will die at the GPU's local handler, until the Q#C6 predicate is exactly right. Predicted highest-likelihood finding.
4. Popup placement edge cases — bottom-of-window flip, gutter offset, narrow windows. Clamping bugs, MenuView-class.
5. The Q#C9 single-char heuristic holds. Paste/undo/kill/remote edits stay quiet and ordinary typing always opens. If validation shows misfires, the fix is the named hook-payload PR, not heuristic patching.

Deferred (named, not silently dropped)

• Snippet tabstops/placeholders (v1 inserts bodies literally).
• completionItem/resolve (lazy documentation/detail) and additionalTextEdits (auto-import) — needs a resolve round-trip on selection change.
• A documentation panel beside the popup (company-style doc buffer).
• Fuzzy matching beyond the current prefix/word-boundary/substring scorer.
• TUI/GPU visual unification (GPU leads, as with the minibuffer).
• Minibuffer-style persisted ranking / frequency weighting.