gate(checklist): bind the platform-checklist corpus to the ONE symbol resolver (#16898)

`scripts/check-platform-checklist.mjs` resolved symbol anchors with a rule of
its own -- mask comments, then ask whether the bare token appears anywhere in
the file -- in the place `scripts/symbol-anchors.mjs` states the #13556 ruling
it implements: "One resolver." The private rule was the LOOSER of the two, so
it resolved anchors the shared resolver refuses and the checklist reported
coverage it did not have; a second resolver that is greener than the shared one
is never the one anybody points at.

`absentAnchorSegments` now delegates every segment to
`symbol-anchors.mjs#symbolResolutionClass` and holds no matcher at all. The
per-segment split stays -- that is this corpus's anchor grammar, not a rule
about what "present" means -- and a self-test assertion reads this file's own
source to pin the body against re-forking.

Withdrawing the permissive match is the deliverable, not a regression: 56 of
633 anchor occurrences stopped resolving (577 resolve -- 516 declaration, 61
literal). All 56 are carried in `SHARED_RESOLVER_RESIDUAL`, one closed row per
(family file, anchor), each with the shape that used to resolve it and a
verdict: 47 bad-citation, 8 accept-set. Every row must fire (a stale row reds),
an unlisted failure is an ordinary red, and a grow-never ceiling sits beside
it -- so the ledger is a closed list that shrinks by repair, never a rule.

No floor is lowered and the maintainer-only baseline is untouched.
`scripts/symbol-anchors.mjs` is untouched too: widening the shared core to keep
this ledger green would export the looser reading to the ADR, `scripts/**`,
spec-docblock and system-context corpora.

Two self-test assertions that pinned the permissive behaviour are RE-JUDGED in
place with the reason recorded, never deleted: P3 (an inline object-literal
member) and P5 (a `.json` value). The directions they really covered are kept
as P3b and P5b on shapes the shared rule accepts.

Co-Authored-By: Claude <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012GKcPZbMoGq7WPzKLfRBTU

Author: claude

docs/qa/platform-checklist/README.md

@@ -173,13 +173,31 @@ Why this shape:
   ```
 
   `check:platform-checklist` resolves every anchor: the file must be in this repo and the
-  symbol must still be in it, **comments masked** — a symbol surviving only in a docblock
-  is ABSENT, because prose about a symbol is not a symbol. A symbol inside a string
-  literal counts as present: much of what this ledger cites *is* a string (capability
-  names, error codes, `sys_*` machine names). Dotted anchors resolve segment by segment.
-  This is presence-in-code, not a declaration analysis — what it catches is the rename or
-  deletion that leaves the pointer naming nothing, which is exactly the rot the line
-  numbers used to carry.
+  symbol must still be **declared** in it. ⭐ The rule is **not this gate's** and not this
+  paragraph's — it is the one shared resolver every anchor corpus in this tree uses
+  (`scripts/symbol-anchors.mjs#symbolResolutionClass`), and that module's own
+  `THE RESOLUTION RULE` block is the authority. What an author needs from it:
+
+  - **comments are stripped first** — a symbol surviving only in a docblock is ABSENT,
+    because prose about a symbol is not a symbol;
+  - a **declaration site** resolves (a `function` / `class` / `interface` / `type` /
+    `const` / `let` / `var`, a member or object-literal key written **at the start of a
+    line**, a named re-export). For a `.json` target that means a **key**, never a value;
+  - a **complete quoted string token** resolves — `'sys_metadata'` — which is what keeps
+    the machine names this ledger is full of anchorable (capability names, error codes,
+    `sys_*` object and field names);
+  - ⚠️ and nothing else does. A **call site**, an **import**, a **member access on some
+    other object**, a **local parameter**, or the symbol appearing only as a **substring
+    of a longer string** (`saveItem` inside `'meta.saveItem'`, `:shareId` inside a route
+    pattern) is **NOT** resolution. If that is all the cited file has, the citation is
+    naming the file that *uses* the symbol, not the file that *declares* it — re-point
+    it, or cite the file bare.
+
+  Dotted anchors resolve segment by segment. ⛔ An anchor the shared resolver refuses is
+  either a bad citation or a case for widening that shared core, and the second is its
+  own card against that module — ⛔ never a local rule here: the core is shared with the
+  ADR, `scripts/**`, spec-docblock and system-context corpora, and widening it to suit
+  this ledger would export the looser reading to all four (#16898).
 - **A citation the gate cannot resolve stays BARE — that is honest, not a gap.** Anchors
   are only for extensions the gate reads symbols out of (`.ts .tsx .mts .cts .js .mjs
   .cjs .json`); an anchor on a `.md` or a `.yml` is an ERROR rather than a silent skip,