docs(rest): retire the stale crash-divergence note on armSentence

Contract review F1: the "What this deliberately does NOT decide" block in
`armSentence`'s docblock still described the pre-#15071 world, and after this
PR every clause of it was false. It said a sandboxed CRASH reaches an arm and
is answered at the arm's own declared status, that the divergence against the
unwrap door's sanitised 500 is UNCHANGED, that the pin records it as an
accepted divergence, and that it "carries its own decision card" -- while the
card is this one and it has been executed: the crash terminal now sits above
the code-gated arms, so no crash reaches this function on either door.

Rewritten as a cross-reference rather than a second statement of the ruling.
`isSandboxCrash`'s own docblock carries the maintainer ruling, its fence and
its negative control; a file that states one rule twice is the drift this
finding is made of, so the block now points there and stops.

The second paragraph keeps the surviving divergence visible: what converged is
the no-declared-status case. A crash that DECLARED a 4xx still leaves
`resolveErrorResponse` at that status with the QuickJS wrapper, through a
passthrough this card did not touch -- pinned as an ACCEPTED DIVERGENCE in
`error-response-structured-arm-door-parity.test.ts`. The prose must not read as
"all divergence is gone", because it is not.

Comment lines only -- no executable byte moves. Proven at parser level: both
revisions re-printed with `removeComments: true` hash identically
(sha256 5daab82cdd23e0b93a1dfb420b2a9e3c83786975248504bdbf9907b321005fa7),
with a control leg that flips one identifier and is correctly rejected.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015QE8qk46e5CHJxyQEUjbf8

Author: claude

packages/rest/src/error-response.ts

@@ -307,16 +307,22 @@ export function sandboxBusinessMessage(error: any): string | undefined {
  *
  * ## ⛔ What this deliberately does NOT decide
  *
- * A sandboxed **CRASH** (#7543). {@link sandboxBusinessMessage} declines one by
- * contract, so the fallback hands the arm `error.message` — the wrapper — and
- * the arm answers with its own declared status, where the unwrap door's
- * terminal for the same crash is the sanitised 500. That divergence is
- * UNCHANGED by this rule, on purpose: choosing between those two answers is
- * fault classification rather than message sourcing (triage on #14704, verbatim:
- * "leave today's behaviour exactly as it is, implement the business-message
- * read only, and name the site and the divergence"). It is pinned in
- * `error-response-sandbox-arm-message.test.ts` §4 so that deciding it is a
- * visible edit rather than a drift, and it carries its own decision card.
+ * Fault classification. A sandboxed **CRASH** (#7543) no longer reaches this
+ * function at all: #15071 put {@link isSandboxCrash} ABOVE the code-gated arms
+ * in {@link classifyDataError}, so a crashed body is answered by
+ * {@link UNCLASSIFIED_FAULT} whatever code it declared, and the other door
+ * declines the consult for a sandbox producer outright (the section above).
+ * ⛔ The ruling that decided it, its fence and its negative control are stated
+ * ONCE, on {@link isSandboxCrash} — read them there rather than a second time
+ * here. `error-response-sandbox-arm-message.test.ts` §4 records the verdict,
+ * now CONVERGED. {@link sandboxBusinessMessage} still declines a crash by
+ * contract, so this function keeps no opinion of its own about one.
+ *
+ * ⚠️ CONVERGED is the no-declared-status case, not the whole question: a crash
+ * that DECLARED a 4xx still leaves {@link resolveErrorResponse} at that status,
+ * wrapper and all, through a passthrough this card did not touch — pinned as an
+ * ACCEPTED DIVERGENCE, widened by #15071, in
+ * `error-response-structured-arm-door-parity.test.ts` §4.
  *
  * ⛔ Deliberately a READ of the field the sandbox populated, never a
  * pattern-strip of the wrapper off `.message` — {@link sandboxBusinessMessage}