Add a gated Known Limitations and Deferred Work section to every package README

Every packages/*/* README now carries a canonical '## Known Limitations and
Deferred Work' section: condensed, evidence-backed bullets for consumer-visible
gaps (unimplemented features, platform caveats, MVP cuts) and consciously
postponed work (TODO/FIXME/XXX markers, RFC deferrals still open). The ten
pre-existing ad-hoc variants ('What is NOT here (TODO)', 'Deferred',
'Limitations (MVP)', 'Known limitations (tracked TODOs)', ...) are normalized
into the canonical heading.

A new doc-sync gate, scripts/verify-readme-limitations.ts, enforces the shape:
exactly one limitations-like heading per package README, byte-equal to the
canonical h2, with at least one bullet; near-miss headings fail so variants
cannot creep back. Packages with genuinely nothing to declare (dsh-brand,
dsh-timeout, dsh-subagent-mock, dsh-app-boot) are whitelisted in the script and
must NOT carry the section; whitelist entries are validated against the scanned
package set so a rename fails loud.

Wired into the doc-sync chain (package.json) and the run-gates doc-sync leaf
set; the standing rule lands in packages/AGENTS.md and the adding-a-package
cookbook; decision record in
docs/rfc/implemented/process/2026-07-10-readme-known-limitations-gate.md
(RFC index regenerated).

Also fixes two stale '(deferred)' markers claiming dsh-compact-basic is
unimplemented (the dsh-compact seam README's package table and the seam's
module doc comment).

packages/guard/repeat-tool-guard/README.md

@@ -35,3 +35,12 @@ Reminders ride the post-execute decision's `additionalContext` (source `{kind: '
 ## Testing
 
 Unit suites drive a real agent loop against a mock adapter (no network) and cover the chain semantics above to per-file 100%. The snapshot tier owns the transcript surface: a scripted-replay scenario repeats a call five times and pins both reminder tiers (gentle at 3, detailed at 5) as `context/message`s in the ACP transcript.
+
+## Known Limitations and Deferred Work
+
+- **Exact-match detection only** — canonicalization is a deep key-sort, so near-identical variants (a tweaked path, extra whitespace inside a value) evade the chain; fuzzy matching is rejected pending evidence of need.
+- **Compaction does not reset chains** — a chain spanning a compaction checkpoint keeps counting.
+- **Advisory only** — escalating to `block` at a high threshold is not implemented, though `PostToolDecision` already supports blocking.
+- **No subagent chain-sharing** — chains stay isolated per agent; a parent and its subagent repeating the same call never combine.
+- **Legitimate idempotent polling still draws nudges** past the thresholds — the pressure valves are `thresholds`/`exclude` config.
+- **Past the highest threshold a chain goes silent** — reminders fire only at exact configured counts, never beyond them.