refactor(examples): extract the app spine into dsh-agent-core + app packages

Implements docs/rfc/.../2026-06-20-extract-example-app-packages.md. Each
example was thick — a hand-rolled start.ts, an infra preamble, nested
base.yml/base-core.yml/acp-tail.yml includes, and a coupled front-door
cluster enforced only by prose. This moves the composition into packages so
each example is a thin leaf cordis.yml: pick the swappable backends, load one
app package.

New packages:
  - @deepseek-ai/dsh-agent-core (packages/core/agent-core): one bundle plugin
    that loads the providerless/executor-less/UI-less spine (timer + llm +
    sessions + system-prompt + tools + agents + invariants + tool-bash +
    agent-loop) via ctx.plugin(...) inside apply(), and forwards agent-loop's
    `agents` list as its own Config (export const Config = AgentLoop.Config,
    default []).
  - @deepseek-ai/dsh-stdio-agent (packages/ui/stdio-agent): terminal chat APP —
    agent-core + console logger + readline UI + a pre-created `main` agent, with
    a bin. The demo:echo/coding front door.
  - @deepseek-ai/dsh-acp-agent (packages/ui/acp-agent): ACP server APP —
    agent-core + JSONL persistence + the acp bridge, NO stdout logger, with a
    bin. The stdout-purity footgun is structurally unreachable from the leaf.

Amendment to the RFC: hmr stays a LEAF cordis.yml entry, not baked into
dsh-stdio-agent. hmr is a Loader-only dev plugin (throws without
--expose-internals; the in-process test tier can't even import its decorator
form), so a package statically importing it could never carry the per-file
coverage gate. Unlike the console logger, a stray hmr is not a stdout-purity
footgun, so leaving it at the leaf costs no safety. With hmr out, all three new
packages carry in-process unit specs at 100%.

Boot glue (Loader tail, .env load, snapshot-mode selection, stdin-dispose
lifecycle) moves into each app's bin; start.ts and base.yml/base-core.yml/
acp-tail.yml are deleted. Each app package gets a keyless real-load-path test
that boots through its bin + the cordis Loader (guarding the unwrapExports
export-shape bug class, postmortem 0001). ACP snapshot replay stays green
against the existing committed goldens (pure boot restructuring). RFC moved
proposed->implemented with the amendment recorded; package/example/architecture
docs and the module graph updated.

packages/ui/acp-agent/src/bin.ts

@@ -0,0 +1,100 @@
+#!/usr/bin/env node
+/**
+ * The `dsh-acp-agent` bin: boot the ACP server from a leaf `cordis.yml` that
+ * loads the {@link @deepseek-ai/dsh-acp-agent} app plugin (plus an LLM adapter
+ * and a bash executor), speaking ACP JSON-RPC on stdio.
+ *
+ * Owns the ACP-specific boot glue the example's `start.ts` once held:
+ *  - `.env` loading (`DEEPSEEK_API_KEY` / `DEEPSEEK_BASE_URL`) — SKIPPED in
+ *    snapshot REPLAY so a stray key can never trigger a live model call.
+ *  - snapshot-mode config selection: `DSH_SNAPSHOT=replay` swaps the given
+ *    `cordis.yml` for its sibling `cordis.snapshot.yml` (the keyless replay
+ *    tree: `llm-replay` in place of `llm-deepseek`).
+ *  - the stdin-dispose lifecycle: in a snapshot run the harness closes stdin
+ *    when done, so dispose the context (flushing persistence) and exit cleanly.
+ *
+ * IMPORTANT: stdout is the ACP JSON-RPC channel. This bin writes diagnostics to
+ * STDERR only; the app plugin loads no stdout logger. A stray stdout write
+ * corrupts the protocol frames.
+ *
+ * Usage: `dsh-acp-agent [path-to-cordis.yml]` (default `./cordis.yml`).
+ *
+ * @module @deepseek-ai/dsh-acp-agent/bin
+ */
+
+import { pathToFileURL } from 'node:url'
+import { basename, dirname, resolve } from 'node:path'
+import { Context } from 'cordis'
+import Loader from '@cordisjs/plugin-loader'
+
+/**
+ * Resolve the config to boot, honoring snapshot REPLAY. Given the requested
+ * path, replay mode swaps a `cordis.yml` basename for `cordis.snapshot.yml` in
+ * the SAME directory (the keyless replay tree). Other modes use the path as-is.
+ * Returns an absolute path resolved from the cwd.
+ */
+export function resolveConfigPath(configPath: string, snapshotMode: string | undefined): string {
+  const absolute = resolve(process.cwd(), configPath)
+  if (snapshotMode !== 'replay') return absolute
+  const dir = dirname(absolute)
+  const replayName = basename(absolute).replace(/cordis\.ya?ml$/, 'cordis.snapshot.yml')
+  return resolve(dir, replayName)
+}
+
+/**
+ * Load `DEEPSEEK_API_KEY` / `DEEPSEEK_BASE_URL` from a gitignored `.env` in the
+ * cwd (Node native). Diagnostics go to STDERR (stdout is the protocol). In
+ * REPLAY mode the caller skips this entirely — replay must never reach the
+ * network, so a present `.env` must not enable a live call.
+ */
+function loadEnv(): void {
+  try {
+    process.loadEnvFile(resolve(process.cwd(), '.env'))
+  } catch (error) {
+    if ((error as NodeJS.ErrnoException | null)?.code !== 'ENOENT') {
+      process.stderr.write(`dsh-acp-agent: failed to load .env: ${String(error)}\n`)
+    }
+    // ENOENT (no .env) is fine — rely on the ambient environment.
+  }
+}
+
+/**
+ * Boot the Loader against `absoluteConfigPath`. `baseUrl` is pinned to the
+ * config's directory and the include gets only the basename, so the config's
+ * relative plugin/include paths resolve as the upstream `cordis` bin does.
+ * Returns the root context.
+ */
+export async function boot(absoluteConfigPath: string): Promise<Context> {
+  const ctx = new Context()
+  ctx.baseUrl = pathToFileURL(dirname(absoluteConfigPath)).href + '/'
+  await ctx.plugin(Loader)
+  await ctx.loader.create({
+    name: '@cordisjs/plugin-include',
+    config: { path: `./${basename(absoluteConfigPath)}` },
+  })
+  return ctx
+}
+
+/**
+ * Entry point. Selects the config (snapshot-aware), loads `.env` outside replay,
+ * boots, and — in a snapshot run — disposes the context on stdin EOF so the
+ * session log is fully flushed before exit and the harness's `waitForExit`
+ * resolves. In a normal editor session stdin stays open for the connection's
+ * lifetime (the editor kills the process), so the EOF handler never fires.
+ */
+export async function main(argv: string[] = process.argv.slice(2)): Promise<void> {
+  const snapshotMode = process.env.DSH_SNAPSHOT
+  const configPath = resolveConfigPath(argv[0] ?? './cordis.yml', snapshotMode)
+  if (snapshotMode !== 'replay') loadEnv()
+  const ctx = await boot(configPath)
+  if (snapshotMode !== undefined) {
+    process.stdin.on('end', () => {
+      void ctx.fiber.dispose().then(() => { process.exit(0) })
+    })
+  }
+}
+
+/* v8 ignore start -- top-level CLI invocation; the testable core is
+   resolveConfigPath()/boot()/main(), driven by the keyless snapshot + Loader-path tests */
+await main()
+/* v8 ignore stop */