docs: move execa Agent Note to implemented; update inbound links and README contracts

- proposed/testing -> implemented/testing with the lifecycle rewrite
  (Proposal->Decision in present tense, Acceptance criteria + Risks
  folded into Consequences); zh counterpart mirrored and both pairs
  re-recorded.
- the rejected NIH-audit roll-up pair now links the implemented/ path.
- loader-smoke README: captured output is bounded by execa's default
  100 MB maxBuffer, no longer unbounded.
- acp-snapshot README: harness.ts now also imports vitest (vi.waitFor),
  so the vitest-run-only constraint names both modules.
- jsonrpc keyless smoke: raise the invalid-env case's subprocess
  deadline to 25s (the 9s pick starved a cold tsx boot on slow NFS).

packages/support/loader-smoke/README.md

@@ -19,5 +19,5 @@ None; this package neither assembles nor sends a provider request.
 ## Known Limitations and Deferred Work
 
 - **Built mode requires a prior build** — the config must also resolve every named package upward through `examples/node_modules`.
-- **Captured stdout and stderr are unbounded** — a runaway child can consume memory until the deadline kills it.
+- **Captured stdout and stderr are bounded only by execa's default 100 MB `maxBuffer`** — a runaway child is terminated at that ceiling rather than at a smoke-chosen budget.
 - **Timeout kills only the direct child** — a process tree spawned by a faulty fixture can outlive the smoke and needs external cleanup.