refactor: unify the Code Mode demos on base-plus-overlay

Both demo:code-mode UIs now share one mechanism: the base example plus a
same-shaped code-mode.cordis.yml include overlay (insert the worker
runtime, flip tools.mode). Previously the REPL side was a hand-forked
example (examples/code-agent) that had also silently diverged — it
dropped compaction and the subagent stack — so the demo's UI argument
switched agents, not just surfaces. The fork is retired: coding-agent
gains the overlay, a Code Mode README section absorbing code-agent's,
and both of its tests (the keyless boot guard, retargeted at the
overlay; the with-key RFC proof, which hand-mounts its own harness and
moves untouched). The RFC's composed-surface and e2e-tier lines, the
examples index, the AGENTS.md smoke table, and the dsh-tools README
link now describe the overlay shape.

Verified live: overlay keyless smoke, with-key code-mode e2e from its
new home, demo:code-mode banner + EOF exit, and the acp handshake.

docs/rfc/implemented/feature/2026-06-15-code-mode.md

@@ -90,7 +90,7 @@ What exists now:
 
 - **The seam**: `packages/code-runtime/` — `@deepseek-ai/dsh-code-runtime` (abstract `CodeRuntime`, the vocabulary above, `ctx.codeRuntime`) and `@deepseek-ai/dsh-code-runtime-worker` (the worker-thread backend, every cap a validated config field). Rows in the service map, capability-seams graph, config catalog, and cordis catalog.
 - **The registry surface**: `ToolRegistry`'s first config (`mode`), the mode-aware wire contribution, the `tools:sdk` section, `jsonSchemaToTs`/`renderToolsSdk` (exported), `run_code` + the dispatch bridge + `CodeRunFailedError`, and the `tool/code-dispatch` log event (declaration-merged into `SessionEventMap`, regenerated into the persistence catalog; `run_code` in the tool catalog).
-- **The composed surface**: the `tools` config forwards through `agent-core` and both app packages (`stdio-agent`, `acp-agent`); `examples/code-agent` + `demo:code-mode` run the worker runtime under `mode: 'code'`; the adding-a-tool cookbook states that a registered tool is reachable from programs for free, and the tool-pipeline doc shows sub-dispatches re-entering both waterfalls.
+- **The composed surface**: the `tools` config forwards through `agent-core` and both app packages (`stdio-agent`, `acp-agent`); `demo:code-mode` boots each UI example's `code-mode.cordis.yml` overlay (the worker runtime + `mode: 'code'` over the base tree); the adding-a-tool cookbook states that a registered tool is reachable from programs for free, and the tool-pipeline doc shows sub-dispatches re-entering both waterfalls.
 - **Interactions inherited by deployments**: a `toolOrder` naming native tools rejects every assembly under `'code'` (update or drop the order config when switching modes); sub-call `additionalContext` is dropped by the bridge (a plural context channel is deferred until a real hook needs it through Code Mode); sub-dispatch stays serialized until tools can declare concurrency safety — the same metadata the native parallel-dispatch TODO waits on.
 
 ## Testing
@@ -99,7 +99,7 @@ What the suites pin, per tier:
 
 - **Unit — worker runtime** (real workers, no mocks): output/value capture and log-source attribution; error kinds (exception incl. non-erasable syntax, abort, worker-exit under OOM); the two budgets from both sides (a hot loop behind an un-awaited pending dispatch dies at `computeMs` busy time; a program idling on a slow binding outlives `computeMs` and dies only at `maxWallMs`); binding-bridge hostility (junk/forged port traffic incl. non-object messages and forged `log`/`done` cap bypass attempts, unknown names, duplicate ids, post-settlement replies, `__proto__`/`constructor`/`toString` binding names); structured-clone fallback and cap truncation; `env` emptiness verified from inside a program; dispose-awaits-exit. A real-load-path e2e runs the BUILT package under plain `node` so the worker entry resolves both unbuilt (tsx) and built — the published-artifact guard from [docs/testing.md](../../../testing.md).
 - **Unit — registry integration**: the codegen table (DSL subset, quoted names, `unknown` degradation, byte-identical determinism); provider contribution per mode (`'native'` unchanged, `'code'` exactly `[run_code]`, `'both'` all + `run_code`); `toolOrder × mode` rejection; missing-runtime / wrong-language loud failures; serialization non-overlap (a probe tool records enter/exit under `Promise.all`); abort aborting the in-flight sub-dispatch and abandoning queued ones; binding rejection on `isError` and on JSON-unrepresentable arguments; `CodeRunFailedError` → structured `isError` carrying kind + logs; `tool/code-dispatch` payloads (JSON-normalized arguments identical to what dispatched); `deriveMessages()` ignoring the event; sub-call `additionalContext` suppression; HMR safety (disposing the registry removes the tool and the section).
-- **e2e (with-key, self-skips)**: a real model under `mode: 'code'` composes two bash calls in one program (`examples/code-agent/tests/code-mode.e2e.ts`) — every logged `request/header` carries exactly `[run_code]`, the dispatch events land under the parent call, the file the program wrote exists, and the final answer is the curated output.
+- **e2e (with-key, self-skips)**: a real model under `mode: 'code'` composes two bash calls in one program (`examples/coding-agent/tests/code-mode.e2e.ts`) — every logged `request/header` carries exactly `[run_code]`, the dispatch events land under the parent call, the file the program wrote exists, and the final answer is the curated output.
 - **Snapshot (keyless replay)**: goldens for a `run_code` turn under `'code'` and `'both'` (`code-mode-turn`, `both-mode-turn`), each its own header-pinning class — the SDK section text, the collapsed header tool list, the dispatch events, and the result card are committed and replayed.
 
 ## Alternatives considered