refactor(examples): extract reusable logic into tested packages

Logic that lived under examples/ was outside the per-file 100% coverage
gate (examples/ are not workspaces) and, in the stdio-UI case, duplicated
across two examples. Move it into packages/ so it is gated and de-duped.

- packages/ui-stdio (new): unify the two diverged stdio-chat.ts copies into
  one @deepseek-ai/dsh-ui-stdio plugin (welcome/agent Config). A test-only
  I/O seam (createStdioChat(ctx, config, runtime)) keeps process streams out
  of the serializable config and makes every render/EOF/disposal branch
  unit-testable. Per-file 100%. echo/coding cordis.yml now load the package;
  both src/stdio-chat.ts deleted.
- packages/llm-replay (new): move examples/acp-agent/src/llm-replay.ts (+ its
  spec) here so its derive/parse/replay branches fall under the coverage gate.
  cordis.snapshot.yml + README rewired to the package name; added apply/env
  /assertNever/abort tests to reach per-file 100%.
- examples/{echo,coding}-agent: keyless Loader-path e2e smokes that boot the
  real cordis.yml (no key) — the guard a hand-mounted unit test cannot be for
  the unwrapExports/export-shape class (postmortem 0001). examples/AGENTS.md
  codifies the keyless+with-key smoke convention (keyless-by-nature exception
  for echo-agent).
- AGENTS.md: a scoped, removal-triggered pre-release stance (foundation over
  blast radius). packages/README.md: new rows + a FIXME to later regroup ALL
  packages into a hierarchy. Wiring: tsconfig paths/refs, publint, knip,
  module-graph.

Verified: typecheck, lint, test:coverage (887 tests, 100%), build, hygiene,
doc-sync, test:snapshot (10), test:e2e (6 keyless pass, with-key self-skip).

packages/README.md

@@ -2,6 +2,14 @@
 
 Harness packages, all under the `@deepseek-ai/dsh-*` scope. Each package is a Cordis plugin (microkernel-style): it exports either a default `Service` subclass or a functional plugin that gets registered via `ctx.plugin()`, declares its ctx key/events where applicable through declaration merging, and exposes extension points through `ctx.effect()`, `ctx.on()`, and `ctx.waterfall()`.
 
+<!-- FIXME(package-hierarchy): packages/ is currently FLAT, mixing product
+     packages (llm, session, agent, agent-loop, …) with example-coupled support
+     packages (ui-stdio, llm-replay — extracted from examples/ for the coverage
+     gate). ALL packages should eventually be regrouped into a deliberate
+     hierarchy, e.g. packages/{core,examples,…}/, so the workspace-glob and
+     tsconfig-paths churn happens ONCE rather than per extraction. Deferred to a
+     dedicated restructure PR; do not add new top-level subgroups piecemeal. -->
+
 ## Dependency graph
 
 ```
@@ -18,6 +26,8 @@ dsh-llm-pi-ai     ← dsh-llm                        (pi-ai-backed adapter)
 dsh-agent-loop    ← dsh-llm, dsh-session, dsh-system-prompt, dsh-tools, dsh-agent
 dsh-invariants    ← dsh-llm, dsh-session, dsh-agent (dev-mode contract checks)
 dsh-acp           ← dsh-agent, dsh-llm, dsh-session, dsh-session-persistence  (ACP JSON-RPC bridge)
+dsh-ui-stdio      ← dsh-agent, dsh-llm, dsh-session (stdio readline UI plugin)
+dsh-llm-replay    ← dsh-llm, dsh-session            (record/replay adapter for keyless snapshot tests)
 ```
 
 The rule: plugins depend on interfaces, never on the concrete loop. `dsh-agent-loop` is swappable — UI/hook/tool plugins keep working against the `dsh-agent` vocabulary if the loop is replaced. A swappable capability splits into interface / implementation / consumer packages (the bash trio is the template — see [capability seams](../docs/rfc/implemented/2026-06-13-capability-seams.md)).
@@ -39,6 +49,8 @@ The rule: plugins depend on interfaces, never on the concrete loop. `dsh-agent-l
 | `llm-pi-ai/` | DeepSeek adapter via `@earendil-works/pi-ai` (design twin) | (registers on `ctx.llm`) |
 | `invariants/` | Dev-mode event-contract invariants + session-log freeze | (listens on `session/*`, `agent/*`) |
 | `acp/` | Agent Client Protocol bridge: serves the agent to an ACP editor over JSON-RPC stdio | (drives `ctx.agents`/`ctx.sessions`) |
+| `ui-stdio/` | Minimal stdio (readline) UI plugin: renders `agent/*` events, feeds stdin lines to the agent | (drives `ctx.agents`) |
+| `llm-replay/` | Record/replay adapter: short-circuits `llm/stream` with chunks from a recorded session JSONL (keyless snapshot tests) | (listens on `llm/stream`) |
 
 Each package has its own `README.md` with purpose, service API, events, extension points, and deliberate non-goals (TODOs).