Phase 3: LLM grammar checkpoint

Backend (internal/llm): backend-agnostic LLMClient interface + factory
with vLLM (OpenAI-compat) and Ollama (native) clients, each Complete +
Stream. prompts.go holds the checkpoint and Ask Petal templates;
checkpoint.go salvages JSON from model output (brace-matched), enforces a
per-doc 30s RateLimiter, and truncates the doc to a latency cap.

internal/suggestions: POST /api/docs/:id/check runs a checkpoint and
replaces the doc's pending suggestions in one tx (accepted/rejected kept
as history); GET /api/docs/:id/suggestions lists pending;
POST /api/suggestions/:id/{accept,dismiss} resolves one. Throttled checks
return the current set rather than erroring.

Frontend: useCheckpoint (4s debounce, loads existing on open, stale-guard
tokens); SuggestionHighlight renders ProseMirror decorations re-anchored
by the `original` string on every doc change (not stored marks), with
precise textblock-offset→PM-position mapping; SuggestionCard shows the
type tag + diff + explanation and applies the replacement in-editor on
accept; breathing rose checkpoint dot in the StatusBar; fade-float +
breathe animations.

Tests: llm parse/rate-limit/truncate; suggestions full flow + rate-limit
over httptest with a stub client. Smoke-tested end-to-end against a fake
vLLM endpoint (anchoring verified) and the LLM-unreachable 502 path.

Claude-Session: https://claude.ai/code/session_016Yr6jELuRc7hyzYLccQKZd

BUILD_PLAN.md

@@ -36,14 +36,14 @@ Multi-session build. **Source of truth for what's done and what's next.** Update
 - [x] StatusBar: word count + save status (Editing→Saving→Saved, fades after 3s)
 - [x] Keep `content` (Tiptap JSON) and `content_text` (plain) in sync on save — editor emits both + word_count together
 
-### Phase 3 — LLM grammar checkpoint
-- [ ] `LLMClient` interface + factory (`internal/llm/client.go`)
-- [ ] `vllm.go` (OpenAI-compat), `ollama.go` (native) — both behind interface
-- [ ] `checkpoint.go` (30s/doc rate limit), `prompts.go`
-- [ ] `POST /api/docs/:id/check`
-- [ ] `useCheckpoint` (4s debounce) + checkpoint indicator
-- [ ] SuggestionMark + SuggestionCard (accept/dismiss); **string-anchoring**, not stored pos
-- [ ] Suggestion colors: grammar=mint, phrasing=peach, idiom=lavender, clarity=sky
+### Phase 3 — LLM grammar checkpoint ✅
+- [x] `LLMClient` interface + factory (`internal/llm/client.go`) — chat-model fallback in factory; doc/history truncation helpers
+- [x] `vllm.go` (OpenAI-compat), `ollama.go` (native) — both behind interface; Complete + Stream; no client-level timeout (ctx deadline for Complete, open stream for SSE)
+- [x] `checkpoint.go` (30s/doc `RateLimiter`), `prompts.go` — brace-matched JSON salvage from model output, empty-original drop, type normalization
+- [x] `POST /api/docs/:id/check` (+ `GET /api/docs/:id/suggestions`, `POST /api/suggestions/:id/{accept,dismiss}`) in `internal/suggestions`; replaces pending set per check, leaves accepted/rejected as history; throttled checks return current set
+- [x] `useCheckpoint` (4s debounce) + breathing rose checkpoint dot in StatusBar
+- [x] `SuggestionHighlight` (ProseMirror **decorations**, re-anchored by `original` string on every doc change — not stored marks) + `SuggestionCard` (accept applies replacement in-editor then PATCHes; dismiss)
+- [x] Suggestion colors: grammar=mint, phrasing=peach, idiom=lavender, clarity=sky (honey reserved for voice)
 
 ### Phase 4 — Ask Petal (conversational follow-up)
 - [ ] `POST /api/suggestions/:id/chat` SSE streaming; server-side context injection
@@ -73,3 +73,4 @@ Multi-session build. **Source of truth for what's done and what's next.** Update
 - 2026-06-25: **Phase 0 complete.** Go module + chi server, config loader, React/Vite/Tailwind-v4 scaffold with full design tokens, frontend embedded & served by the binary, verified end-to-end. Toolchain: Go 1.24.4, Node 22, npm 10. Next: **Phase 1 (data layer)** — SQLite via modernc, models, seed `local` user.
 - 2026-06-25: **Phase 1 complete.** `internal/db` package: modernc.org/sqlite (pulled go toolchain → 1.25), `Open()` does mkdir + WAL/foreign-keys DSN + versioned migration runner + idempotent local-user seed. Models with type/status constants. Wired into `main.go`; tests pass (migrate/seed idempotency, CHECK reject, FK cascade). Verified server boots and writes `petal.db`. Next: **Phase 2 (document CRUD + auto-save)** — first "it works" milestone.
 - 2026-06-25: **Phase 2 complete.** Backend `internal/docs`: chi sub-router (list/create/get/update/delete) mounted at `/api/docs`, local-user scoped, RETURNING on create, COALESCE partial-update (one PUT serves rename + full save), 404/400 JSON errors; `handlers_test.go` walks the full lifecycle. Frontend: `api/client.ts`, `useAutoSave` (1.5s debounce + `saveNow` flush), `EditorCore` (Tiptap StarterKit/Underline/TextAlign/Placeholder/CharacterCount) + `Toolbar`, `DocList`/`DocListItem`, `StatusBar`, rewritten `App.tsx` orchestrating load/select/create/delete with optimistic sidebar patching. `.petal-prose` styles (Lora body, Nunito headings). tsc clean, vite build OK, go build OK; smoke-tested full CRUD incl. CJK title round-trip + SPA serve. Next: **Phase 3 (LLM grammar checkpoint).**
+- 2026-06-25: **Phase 3 complete.** Backend `internal/llm`: `LLMClient` interface + factory (vLLM OpenAI-compat + Ollama native, both Complete/Stream), `prompts.go` (checkpoint + Ask Petal templates), `checkpoint.go` (brace-matched JSON salvage, per-doc 30s `RateLimiter`, doc/history truncation). `internal/suggestions`: `/api/docs/:id/check` + `:id/suggestions` + `/api/suggestions/:id/{accept,dismiss}`; each check replaces the pending set in a tx (accepted/rejected kept as history), throttled checks return the current set, positions located by `strings.Index` (advisory only). Frontend: `useCheckpoint` (4s debounce, loads existing on doc open, run-token guards stale responses), `SuggestionHighlight` Tiptap extension rendering ProseMirror **decorations** re-anchored by `original` string on every doc change (precise textblock offset→PM-pos mapping, handles inline atoms), `SuggestionCard` (type-colored tag, original→replacement diff, accept applies replacement in-editor + PATCHes, hover-bridge with close delay), breathing rose checkpoint dot in StatusBar, suggestion fade-float + breathe CSS. Tests: llm parse/rate-limit/truncate, suggestions full flow + rate-limit over httptest with a stub client. go build/vet/test clean, tsc clean, vite build OK; end-to-end smoke-tested against a fake vLLM endpoint (anchoring verified: `I has`→0:5, `two apple`→6:15) and 502 path when LLM unreachable. Next: **Phase 4 (Ask Petal SSE chat).**