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.

docs/rfc/rejected/architecture/2026-06-20-providerless-example-base.md

@@ -1,23 +1,23 @@
 # RFC: Make the shared example base providerless
 
-Status: rejected — superseded by [Extract example apps into packages](../../proposed/architecture/2026-06-20-extract-example-app-packages.md), which moves the spine into a `dsh-agent-core` bundle and deletes the `base*.yml` files, so there is no shared base YAML left to rename.
+Status: rejected — superseded by [Extract example apps into packages](../../implemented/architecture/2026-06-20-extract-example-app-packages.md), which moves the spine into a `dsh-agent-core` bundle and deletes the `base*.yml` files, so there is no shared base YAML left to rename.
 
 ## Problem
 
-The examples have two shared base files: [examples/base-core.yml](../../../../examples/base-core.yml) is providerless, while [examples/base.yml](../../../../examples/base.yml) includes that core plus the real `llm-deepseek` adapter. Snapshot replay needs the providerless core with `llm-replay`, because loading the real adapter without a key throws. The normal demos need the real adapter. The result is a naming inversion: the file named `base.yml` is not the reusable base for all examples, while the true base is `base-core.yml`.
+The examples had two shared base files: `examples/base-core.yml` was providerless, while `examples/base.yml` included that core plus the real `llm-deepseek` adapter. Snapshot replay needs the providerless core with `llm-replay`, because loading the real adapter without a key throws. The normal demos need the real adapter. The result was a naming inversion: the file named `base.yml` was not the reusable base for all examples, while the true base was `base-core.yml`.
 
-The split is understandable, but it makes every config explanation longer. It also leads to awkward test setup like a keyless smoke test carrying a dummy API key so an adapter can boot even though the model is not called.
+The split was understandable, but it made every config explanation longer. It also led to awkward test setup like a keyless smoke test carrying a dummy API key so an adapter could boot even though the model is not called.
 
 ## Proposal
 
-Rename the providerless core to [examples/base.yml](../../../../examples/base.yml) and make adapter selection explicit in each concrete example. The coding and ACP real configs add a tiny `llm-deepseek` include or local block; snapshot config adds `llm-replay`. Delete [examples/base-core.yml](../../../../examples/base-core.yml).
+Rename the providerless core to `examples/base.yml` and make adapter selection explicit in each concrete example. The coding and ACP real configs add a tiny `llm-deepseek` include or local block; snapshot config adds `llm-replay`. Delete `examples/base-core.yml`.
 
 The shared base should contain only provider-neutral services and tools: `llm`, sessions, system prompt, tools, agents, invariants, bash executor, and bash tool schemas. Anything that chooses a model provider belongs at the leaf config.
 
 ## Acceptance criteria
 
-- [examples/base.yml](../../../../examples/base.yml) is providerless.
-- [examples/base-core.yml](../../../../examples/base-core.yml) is deleted.
+- `examples/base.yml` is providerless.
+- `examples/base-core.yml` is deleted.
 - Real demo configs explicitly add the DeepSeek adapter.
 - Snapshot replay config includes the same providerless base and its replay adapter.
 - The [examples README](../../../../examples/README.md), example-specific READMEs, and RFC references stop explaining "base = base-core plus adapter".