docs(phase2): coverage gate, migration TODOs, session handoff

- add tools/check_coverage.py and .audit/coverage ledger (schema + settings pilot)
- add coverage gap worklist and source-doc migration TODOs
- add session handoff; redirect stale resume points in AGENTS.md, docs/README.md, reconciliation record
- add rows: CAPTURE-41, CAPTURE-141, METADATA-66, PUBLISH-31, SETTINGS-51

.audit/coverage/README.md

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+# Coverage ledger
+
+Provenance for every requirement in `docs/REQUIREMENTS.md`. One row per source atom.
+Kept under `.audit/` on purpose, so it is not part of the `docs/` structure contract.
+
+`tools/check_coverage.py` reads every `*.md` in this directory except this file.
+
+## Row format
+
+```
+| Source | Atom | Requirement | Disposition | PoR ID | Rationale |
+```
+
+- **Source** — where the atom came from, prefixed by kind: `tag:TEST-SPEC`, `tag:OPENAPI`,
+  `prd`, `cur:CREATE`, `issue:#5`, `audit:14`.
+- **Atom** — the stable key inside that source, e.g. `H-1`, `settings-PUT-reject`.
+- **Requirement** — a short restatement, enough to recognise it.
+- **Disposition** — one of the values below.
+- **PoR ID** — the `docs/REQUIREMENTS.md` ID(s), comma-separated. `—` when none.
+- **Rationale** — required for everything that is not plain `ported`.
+
+## Dispositions
+
+| Value | Meaning | PoR ID | Rationale |
+|---|---|---|---|
+| `ported` | fully represented by the cited row(s) | required | optional |
+| `duplicate` | same rule as another atom | optional | required |
+| `new` | PoR row with no source atom; a reconciliation decision | required | required |
+| `superseded` | replaced by a later source or decision | optional | required |
+| `deferred` | intentionally out of current scope | optional | required |
+| `dropped` | deliberately discarded | `—` | required |
+| `gap` | not represented, not deliberately dropped: an open hole | `—` | required |
+
+`gap` is the finding. It is the thing this ledger exists to surface.
+
+## Checks
+
+Forward (always):
+
+1. Every row has six well-formed columns and a known disposition.
+2. A `(Source, Atom)` pair is unique across the ledger.
+3. `ported` and `new` cite at least one defined requirement ID; every cited ID resolves.
+4. `dropped` and `gap` carry no ID and a non-empty rationale.
+5. Every non-`ported` row carries a non-empty rationale.
+
+Reverse (`--strict` only, once coverage is complete):
+
+6. Every ID in `docs/REQUIREMENTS.md` is claimed by at least one atom, or is `new`.
+7. No `gap` rows remain.
+
+## Run
+
+```
+python tools/check_coverage.py
+python tools/check_coverage.py --strict
+python tools/check_coverage.py --ledger-dir <path>   # for negative tests
+```