fix(settings-local): never steal writer locks

2026-07-31 01:14:43 +08:00
parent f9f8148e79
commit afb05b4049
9 changed files with 36 additions and 75 deletions
@@ -19,7 +19,7 @@ Defaulting is one explicit `resolveSpec(config)` step; an unsupported extension

 - **Boot fails loud, reload keeps last-good.** An existing-but-invalid document fails plugin load; once live, an unreadable or unparsable edit warns and keeps the last good sections. A missing document resolves every namespace from defaults and `base`; deleting it publishes the same empty state.
 - **Every write is a read-modify-write.** A persist first re-reads the document and publishes any difference into the seam — an external edit still inside the watcher debounce window, a change the watcher missed, or another process's write — then renders against that fresh text, so a write can never resurrect a stale document or drop an unobserved sibling section. If the on-disk document turned invalid, the write rejects loud instead of overwriting the user's manual edit.
- **Writes hold a cross-process writer lock.** The read-render-rename cycle runs under a `wx`-created `<file>.lock` sibling with exponential backoff, a 2 s acquisition deadline (the write rejects), and stale-lock takeover after 5 s (a crashed holder, broken with a warning). Readers never take the lock: the rename commit is atomic, so reloads are always consistent.
+- **Writes hold a cross-process writer lock.** The read-render-rename cycle runs under a `wx`-created `<file>.lock` sibling with exponential backoff and a 2 s acquisition deadline. A contender never removes a lock it does not own; it rejects at the deadline instead. Readers never take the lock: the rename commit is atomic, so reloads are always consistent.
 - **Write-back is atomic, owner-only, and symlink-proof.** The render exclusive-creates a random-suffix temp sibling with mode `0600` (`wx` refuses to follow a planted symlink) and renames over the target, cleaning the temp up on failure.
 - **YAML edits are leaf-level diffs.** A write sets only the values that changed and deletes only the keys that were removed, so comments, anchors, and formatting survive on every untouched node and on the key of every changed pair; a changed array (or other non-map value) replaces wholesale, taking comments inside it along. JSON re-serializes without comments.
 - **Reloads and writes share one operation chain.** Watcher refreshes and persists from every namespace queue run one at a time in queue order; each render sees the text the previous operation committed.
@@ -38,6 +38,7 @@ No direct invalidation; the consuming plugin owns any request-prefix changes.
 ## Known Limitations and Deferred Work

 - **Same-namespace conflicts stay last-write-wins** — the writer lock and read-modify-write keep concurrent writers from dropping each other's namespaces, but two writers editing one namespace still resolve to the later write; there is no per-value merge or revision check.
+- **An abandoned writer lock requires operator recovery** — lock age cannot prove ownership, so writers fail closed after 2 s instead of deleting an old lock that may still protect a slow holder; remove `<file>.lock` only after establishing that no writer owns it.
 - **A missed watcher event stays unseen until the next signal** — reads never re-stat the file, so a change the watcher fails to report is only folded in by the next event, the next write, or a restart.
 - **Comment preservation is YAML-only and map-shaped** — JSON documents re-serialize without comments (JSON has none), and comments inside a changed array (or attached inline to a changed scalar value) go with the value they described.
 - **No value indirection** — sections hold literal values; `${env:VAR}`-style references for secrets are a deferred seam-level feature.