Multi-user groundwork: request-scoped user identity

Petal ran as a single hardcoded user, with db.LocalUserID named directly
at ~35 query sites. That made the caller's identity a compile-time
constant scattered across every package — nothing a real login could
replace without touching all of them.

New internal/auth moves it into the request context:

  - Middleware(Resolver) resolves the caller once per API request
  - handlers read auth.UserID(r.Context()) instead of naming a user
  - Resolver is the seam an Authentik session check drops into
  - StaticResolver(db.LocalUserID) keeps Petal single-user today

Behavior is unchanged. UserID returns "" rather than panicking when the
middleware is absent, so a mis-wired route fails closed: every query is
WHERE user_id = ?, which then matches nothing.

main.go splits /api into a public group (/health, /version) and an
authenticated group for everything else — a monitoring probe must not
need a session.

Two pre-existing access-control gaps fixed while threading, both
harmless with one user and not with two:

  - setStatus (accept/dismiss) updated a suggestion by bare id with no
    ownership check at all
  - listForDoc/fetchPending read a document's suggestions by doc_id
    alone; a suggestion quotes the sentence it corrects, so that leaked
    the source prose

Both now scope through documents.user_id.

Tests: internal/auth covers the context round-trip, the absent-context
case, and both 401 paths. Two-user isolation suites in docs and
suggestions mount the same routers twice behind two resolvers over one
database and assert a stranger gets 404 on every id-taking path, sees
nothing in list/search, and leaves the owner's data untouched.

Those suites earned their keep immediately: docs.fetch gained a userID
parameter but kept binding db.LocalUserID in the query. Unused
parameters are legal Go, so it compiled clean, vet was silent, and every
existing test passed while the lookup stayed unscoped.

Still global, out of scope and flagged in BUILD_PLAN.md: the image store
has no per-user association, and frontend localStorage keys are
per-browser rather than per-account.

BUILD_PLAN.md

@@ -135,7 +135,8 @@ Multi-session build. **Source of truth for what's done and what's next.** Update
 - [x] Verified: tsc clean, vite build OK, companion vitest 45/45. **Real-browser screenshots** (local Playwright + Chromium, clock mocked to 23:30): day = warm cream + pink sakura petals; night = dark plum-indigo + twinkling stars + glowing sleepy kitten. Both pretty (acceptance criterion).
 
 ### Deferred (post-v1-local)
-- [ ] Authentik OIDC auth + session middleware  ← **on hold: user doing foundational work first**
+- [x] **Multi-user groundwork** (2026-07-26) — request-scoped identity. New `internal/auth`: `Middleware(Resolver)` resolves the caller once per API request and stores the id in the context; handlers read it via `auth.UserID(r.Context())` instead of naming `db.LocalUserID`. `StaticResolver(db.LocalUserID)` keeps Petal single-user today. **Auth itself is still deferred** — but every query is now scoped to whoever the resolver says is calling, so landing Authentik is a one-line change in `main.go` plus a `Resolver` implementation.
+- [ ] Authentik OIDC auth + session middleware  ← **next step: write a `Resolver` that validates a session cookie; the plumbing is in place**
 - [ ] Copyleaks Tier-2 + webhook HMAC
 - [ ] Dockerfile, docker-compose, Traefik, deploy to write.parodia.dev
 
@@ -147,6 +148,7 @@ Multi-session build. **Source of truth for what's done and what's next.** Update
 - [x] **Phase 14 — companion warmth + bedtime nag + night mode**: more encouraging phrases, a gentle "go to bed" nudge after 11pm, and a calm dark theme + falling stars at night. ✅ (see Phase 14 above)
 
 ## Session log
+- 2026-07-26: **Multi-user groundwork** (user: "let's start preparing Petal for multi-user support"; scope agreed as plumbing-only, aimed at Authentik). New **`internal/auth`** package — context-carried identity (`WithUser`/`UserID`), a `Resolver` seam (`Resolve(*http.Request) (string, error)`), `StaticResolver` for today's single user, and `Middleware` that 401s anything unresolved. `main.go` splits `/api` into a **public group** (`/health`, `/version` — a monitoring probe must not need a session) and an **authenticated group** carrying everything else. All ~35 `db.LocalUserID` call sites across `docs`/`suggestions`/`vocab` now read the caller from the request; helpers that had no request in scope (`fetch`, `ownsDoc`, `ownsTag`, `tagsByDoc`, `fetchVersion`, `passportVersions`, `fetchPending`, vocab `fetch`) take an explicit `userID` param. `UserID` returns `""` rather than panicking when middleware is absent, so a mis-wired route **fails closed** (every query is `WHERE user_id = ?` → matches nothing). **Two real access-control gaps found and fixed while threading**: `setStatus` (accept/dismiss) updated a suggestion by bare id with **no ownership check at all**, and `fetchPending`/`listForDoc` read a document's suggestions by `doc_id` alone — a leak of the quoted source sentences. Both now scope through `documents.user_id`. **A third bug was caught by the new tests, not by the compiler**: `docs.fetch` gained a `userID` parameter but kept binding `db.LocalUserID` in the query — legal Go (unused params compile), silently unscoped, and it would have shipped. New tests: `internal/auth/auth_test.go` (round-trip, absent-context, both 401 paths) and **two-user isolation suites** (`docs/isolation_test.go`, `suggestions/isolation_test.go`) that mount the same routers twice behind two resolvers over one DB and assert a stranger gets 404 on get/update/delete/export/passport/snapshot/version-preview/restore/tag-assign/tag-rename/tag-delete/suggestion-accept/dismiss, sees nothing in list/search/version-list, and leaves the owner's data untouched. go build/vet/test all clean. **Still global, deliberately out of scope** (flagged for the auth phase): the image store is content-addressed with no per-user association or DB row — any authenticated user holding a hash can fetch any image (capability-URL security, needs a table + migration to fix); `export-all` is correctly scoped; frontend `localStorage` keys (`petal.spell.personal`, `petal.companion`, sound/petals prefs) are per-browser, not per-account, so they'd bleed across users sharing a device.
 - 2026-06-26: **Phases 12 + 13 complete** (collocation coach + vocabulary garden — "finish the rest of the build plan except Authentik/Traefik"). **Phase 12**: collocation drops in as a third suggestion family reusing the whole `runPass`/`pendingScope` machinery — `llm/collocation.go` (`RunCollocation`, 25s floor, reuses `ParseCheckpoint`), `collocationSystemPrompt`/`CollocationMessages` (warm "Natives usually say…" + Mandarin gloss, defers grammar elsewhere), migration `0005` **rebuilds** the suggestions table to extend the `type` CHECK (SQLite can't ALTER a CHECK), `collocationScope` + `CollocationLimit` + `POST /{id}/collocation`. **Caught a latent bug**: `grammarScope` was `type != 'voice'` → would wipe collocation flags; fixed to `type NOT IN ('voice','collocation')`. Frontend: `--color-blossom` pink, "Make it sound natural 🌸" toolbar pill, `collocating`/`runCollocation` in `useCheckpoint`, StatusBar dot — all into the existing rail/card. **Phase 13**: new `internal/vocab` package — migration `0006_vocab_garden` (`vocab_words`, SM-2-lite columns, doc_id `ON DELETE SET NULL`, `UNIQUE(user_id,word)`), `scheduler.go` (Leitner ladder 1/3/7/16/35 → geometric; gentle "again", no streak-shaming), `handlers.go` (capture-upsert/list/due/review/delete, all owner-scoped, time math via SQLite `datetime()` so stored values stay canonical-UTC). Auto-capture wired into `EditorCore.openWordLookup` (only dictionary-known words, captures the surrounding sentence + doc_id) + a 🤍/💚 toggle on `WordCard`. `GardenPanel` slide-over: blossom grid (bloom stage by reps), flashcard review (sentence blanked, flip, again/good/easy, direction alternates recognition↔production), sleepy-kitten footer; opened from a global 🌷 header button. Tests: `TestCollocationPassCoexists`, vocab `scheduler_test.go` + `handlers_test.go`, db CHECK test extended. go build/vet/test + tsc + vite + vitest (51/51) all clean; migration verified against a copy of the live DB; live backend smoke (throwaway DB) walked the full vocab lifecycle + the warm-502 collocation path. **Remaining: only the deferred infra bucket** — Authentik auth, Copyleaks Tier-2 (needs a public webhook), Docker/Traefik/deploy — all on hold per the user's "except Authentik/Traefik".
 - 2026-06-26: **Phase 14 complete** (companion warmth + bedtime nag + night mode). `tips.ts`: `ENCOURAGEMENTS` 5→10 lines; new `BEDTIME` array (4 lines, user-supplied English wit + gentle Mandarin leads). `useCompanion.ts`: bedtime branch in the 10s heartbeat (after idle-return + break, before the generic tip); only nudges while actively writing; own `lastBedtime` ref + 30min `BEDTIME_GAP`, respects `PROACTIVE_GAP`; new `'bedtime'` `BubbleTone` lingers ~4s longer. **Night mode** (added same session, user request): `lib/night.ts` centralizes `isBedtime()` + window (now shared by the nag too); `hooks/useNightMode.ts` toggles `petal-night` on `<html>` (60s re-check); `index.css` `html.petal-night` re-points only the palette tokens → whole UI flips via `var()` (no component edits), 600ms dusk fade, print stays white; `PetalFall` gains a `night` prop → chunky cartoon power stars (`makeCartoonStar`, Mario/Kirby-style, 5 candy colors) mixed ~70/30 with small twinkle sparkles, gentle spin + shallow shimmer, effect re-inits on flip; App: `useNightMode()` → `<PetalFall night={night}/>`. tsc + vite clean, companion vitest 45/45; verified with real-browser Playwright screenshots (clock mocked to 23:30) — day petals/cream vs night stars/dark-plum, both pretty. Bedtime window is `BEDTIME_FROM`/`BEDTIME_TO` (local clock) for easy retune.
 - 2026-06-26: **Phase 11 complete** (writer power-ups, batch requested as "do it all"). Seven features: (1) in-doc **Find & Replace** — `SearchHighlight` decoration extension + `FindReplace` bar (Ctrl/Cmd+F, match-case, replace-all back-to-front, DOM scroll that doesn't trigger the selection bubble); (2) **read-aloud** Web Speech util + 🔊 in WordCard & selection bubble; (3) **keyboard/touch access** — Ctrl/Cmd+D caret lookup, Ctrl/Cmd+J rewrite, touch long-press (refactored `handleContextMenu` → shared `openWordLookup(pos)`); (4) **export-all** backup zip (`GET /api/docs/export-all`, `TestExportAll`, sidebar download links); (5) **smart typography** input-rules extension (curly quotes/em-dash/ellipsis, ASCII-only so CJK untouched); (6) **duplicate doc + sidebar sort + outline popover**; (7) **English phonetic** (pivoted from pinyin — IPA is what an English learner needs; pinyin annotates Chinese she already reads) via `scripts/build_phonetic.py` + embedded `phonetic.json.gz` + `Result.Phonetic` + WordCard `/ˈrɪvər/` line — **full 46,579-word dataset built from ECDICT** (the csv re-download worked; `--seed` mode kept as a csv-free fallback). Also folded in this session: the **selection-bubble vs copy/paste fix** (bubble deferred to pointer-up + container `pointer-events:none` so it never sits where you click). go build/vet/test + tsc + vite all clean; live smoke verified word-phonetic (incl. de-inflection) + export-all zip (de-duped CJK names, route priority). Next: deferred bucket (auth/Copyleaks/deploy), still on hold per user.