feat(acp): show the command in execute titles; test via the real bash tool; RFC for terminal rendering

- bash presentCall title is now "description — command" (e.g. "List files in
  src — ls -la src"). An execute-kind ACP card HIDES rawInput (Zed renders it
  only for non-terminal tools), so the command must ride in the always-visible
  title to be seen — matching how claude-agent-acp/codex-acp title execute
  tools. The command stays in rawInput too for non-execute UIs that show it.
- Rework the acp tool-call presentation tests (turns + load replay) to drive the
  REAL dsh-tool-bash + dsh-bash-local via a new makeBridgeHarness({ withBash })
  option, running an actual `echo` — instead of an inline fake bash tool. The
  mock MODEL still scripts the call (deterministic, no key), but the tool and
  executor are real, so the test verifies the shipping presentCall/presentResult.
- AGENTS.md: add the principle "prefer the REAL implementation over a mock/
  stand-in in tests" (mock only the expensive/non-deterministic boundary).
- RFC (proposed): the ACP terminal sub-protocol + command classification — the
  capability-gated rich rendering (live cwd-header terminal card, classify a
  `cat` as a read / `grep` as a search) that the reference adapters do; the
  fenced ```console text block stays the no-capability baseline. Studied
  codex-acp, claude-agent-acp, and Zed's renderer to ground it.

AGENTS.md

@@ -121,6 +121,7 @@ Dev/test/demo run **unbuilt** via tsx + the `paths` map in the root `tsconfig.js
 - **Merging PRs**: always merge with a **merge commit** (`gh pr merge --merge`), never squash or rebase. The per-PR commit history is intentional — review-fix commits, regression-test commits, and the reasoning in each message are part of the record — and squashing flattens it away.
 - **TODO markers**: use `FIXME`/`TODO`/`XXX` to flag known issues by urgency — see [docs/development.md](docs/development.md) for the semantics of each.
 - **Tests**: vitest, colocated under `packages/<name>/tests/*.spec.ts`. Every registry needs an HMR-safety test (dispose the contributing fiber, assert cleanup). **Excessive tests are welcome** — when in doubt, write the test; err on the side of covering edge cases, error paths, event ordering, and concurrency races even if they seem unlikely. Review findings get regression tests (see `packages/agent-loop/tests/review-fixes.spec.ts`). The same generosity applies to **real-API (with-key) e2e tests — inference is cheap here (we are DeepSeek), so do not ration them**: cover the agent's real flows (a real prompt that writes a file, multi-turn, tool use, cancellation) and run them frequently while developing, especially cheap **smoke tests** that boot the real example and check the world. A green mock/no-key suite proves the plumbing, not the product — the with-key smoke test is what catches "green units, broken product". See § Secrets / .env for the with-key policy and why self-skip is a CI accommodation, not a verdict that real-API tests are expensive.
+- **Prefer the REAL implementation over a mock/stand-in in tests.** When the genuine collaborator is available in the repo, wire it up instead of hand-rolling a fake — a test that registers an inline `defineTool({ name: 'bash', … })` to stand in for `dsh-tool-bash` proves the *bridge* moves bytes but not that the *shipping tool* renders the way the test asserts; the two drift and the test passes while the product is wrong. Mock only the genuinely expensive/non-deterministic boundary (the LLM adapter, the network, the clock) and keep everything downstream real: a bridge tool-call test runs the scripted mock MODEL but the REAL tool + REAL executor (e.g. `makeBridgeHarness({ withBash: true })` plugs `dsh-bash-local` + `dsh-tool-bash` and runs an actual `echo`), so it verifies the actual `presentCall`/`presentResult` an editor sees. This is the unit-test echo of "verify the world, not a synthetic stand-in" (see § Defensive patterns) — a fake you wrote will agree with whatever you assumed; the real thing won't.
 
 ## Defensive patterns (hard-won)