fix(events): address Codex review — protect post-execute result, purge stale tools/execute refs

Codex's PR-C review found two (A) blockers:

- tools/post-execute could corrupt the protected outcome. postExecute passed the
  mutable `result` to listeners and then read result.callId / spread result on the
  return paths, so a listener mutating the reference (flipping isError, rewriting
  callId, injecting an error) escaped the decision channel. Now the authoritative
  callId/isError/error are SNAPSHOT before the waterfall and the return value is
  rebuilt from the snapshot + the typed PostToolDecision — the decision is the only
  sanctioned way to change the outcome, and callId is always exec.callId. Added a
  regression test that mutates the result reference and asserts it has no effect;
  proven to fail red on the unfixed code.

- Public docs/JSDoc still advertised the removed `tools/execute` waterfall after the
  split. Swept every current-state reference to tools/pre-execute + tools/post-execute:
  the ToolRegistry class JSDoc (and the regenerated catalog), loop.ts's ASCII flow
  (also added the prompt-submit/session-start steps it was missing), the package-map
  READMEs (packages, core, agent-core), core-data-structures core.md/tools.md, the
  bash + acp + invariants src/READMEs (the deferred permission gate is the
  tools/pre-execute deny/ask seam now), the cookbook, and the implemented RFCs whose
  factual seam catalog drifted. codec.ts's totality prose now lists `rejected`.
  Proposed-RFC references are left as-is (frozen proposals, validated when built).

packages/core/agent-core/README.md

@@ -13,7 +13,7 @@ This is the package to read to see **the whole plugin tree at once** — the tea
 @deepseek-ai/dsh-llm              abstract LLM service + content-block vocabulary
 @deepseek-ai/dsh-session          event-sourced session log + store
 @deepseek-ai/dsh-system-prompt    prompt-section + tool-schema assembly
-@deepseek-ai/dsh-tools            tool registry + tools/execute waterfall
+@deepseek-ai/dsh-tools            tool registry + tools/pre-execute/post-execute
 @deepseek-ai/dsh-agent            agent registry + agent/* event vocabulary
 @deepseek-ai/dsh-invariants       dev-mode event-contract assertions
 @deepseek-ai/dsh-tool-bash        the model-facing bash/bash_output/bash_kill schemas