docs(rfc): fold PR #139's simplification sweep into this set

Deduplicate the parallel sweep from codex/exhaustive-simplification-rfcs
(merged in the parent commit) against the twelve RFCs already here, on
the merits per item:

Ported (rewritten to this set's evidence standard):
- fold-stdio-ui-helper — verified: dsh-stdio-agent is the only runtime
  importer; the fold resolves the documented product-app-depends-on-
  support-package tension. The false acp-agent analogy is replaced with
  the real distinction (protocol product surface vs one app's front-door
  scaffolding).
- generate-rfc-index-tables — verified: the classification RFC records
  rejecting generation; the index tables are the repo's only
  systematically conflicting docs region. Process framing made timeless.

Consolidated into existing owners:
- web searchStatus()/fetchStatus()/WebCapabilityStatus (verified: zero
  production callers; the tool-web README and architecture.md claims are
  drift) → drop-web-providers-change-event, renamed
  drop-unconsumed-web-observation-surface.
- hook/result.durationMs (unread, nondeterministic, normalizer-scrubbed)
  and the double-defaulted defaultTimeoutMs knob →
  tighten-hook-protocol-contract.
- the exercised-but-unadvertised exec.arguments mutation path (a
  tool-bash integration shim rewrites through it) → a sanction-or-seal
  note in the pre-tool-input-rewrite proposal.
- the dormant-guard critique of subagent depth machinery → recorded in
  prune-unimplemented-subagent-vocabulary as the considered-and-rejected
  alternative, with the keep sharpened (uncapped-today acknowledged;
  wiring the cap is the completion, not deletion). getProvider()/list()
  and lastAssistantMessage recorded as examined-and-kept (bash-revert
  precedent; observe-enrich recorded keep).

Not ported (with reasons):
- tools/change + system-prompt/change removal — recorded keeps in the
  adapter-change RFC, unengaged by the sweep; no new facts.
- LlmService.models() — flagged by both surveys, but two lines with a
  plausible consumer: TODO-or-drive-by territory per the RFC bar, not
  a proposal.
- SchemaProp.default RFC — already XXX(unused-default)-tagged; the RFC
  bar excludes TODO-tracked provisional cleanups.
- PreToolDecision 'ask' removal — FIXME(permissions)-anchored deferral
  with the permission system as its named consumer.
- Codex bridge Config.model, merged systemMessages — wire-faithful
  tested surface / README-documented deferral.

Their in-code TODO notes (acp-test-harness, hook-snapshot-noise,
catalog-type-links) and the stale hook-prompt-block name fixes ride the
merge unchanged.

docs/rfc/proposed/feature/2026-06-30-pre-tool-input-rewrite.md

@@ -16,7 +16,7 @@ In the loop, a tool call's arguments are committed to the log and read by live c
 2. **`tool/call`** is the durable AUDIT record, appended before `ctx.tools.execute()`.
 3. **Live presentation reads `tool/call.arguments`**: the ACP bridge remembers them and passes them to `presentResult`; `dsh-tool-bash` derives the card title, the rawInput, the cwd, and the terminal-vs-background treatment from them.
 
-So an "input rewrite" that changes ONLY what executes would make the UI show one command while another RAN, and render result state against the wrong arguments — a real inconsistency, not a documentable gap. (The existing low-level capability to mutate `exec.arguments` in a listener has exactly this latent inconsistency; it is unadvertised precisely because of this.)
+So an "input rewrite" that changes ONLY what executes would make the UI show one command while another RAN, and render result state against the wrong arguments — a real inconsistency, not a documentable gap. (The existing low-level capability to mutate `exec.arguments` in a listener has exactly this latent inconsistency; it is unadvertised precisely because of this — yet not unused: a tool-bash integration test rewrites a scripted call's arguments through it (`packages/bash/tool-bash/tests/integration.spec.ts`), so this design must either sanction that path with the consistency unit below or seal it — `readonly` arguments at the seam, with the test shim moved onto a behavior-level helper.)
 
 ## Proposed design (sketch — to validate against the code when built)