fix review findings: harden the app bins + built-bin smokes, arch-exception doc, snapshot fixture-guard

BLOCKER — the published lib/bin.js (stdio + acp) was exercised only via tsx
(demo:* / the src/bin.ts smokes); the built artifact under plain `node` was
unguarded. Root-cause on the BUILT bin:
  1. Settle race: boot() returned once loader.create() registered the include
     ENTRY, but the include loads its child plugins asynchronously — so boot()
     (and main()) resolved while the app plugins (stdin reader, agent loop, ACP
     bridge) were still mounting. A CLI with no attached handles yet exits 0
     silently, and a load error surfaces as an unhandled rejection AFTER boot.
     Fix: `await ctx.loader.await()` after create() — settle the whole tree.
  2. Config-path robustness: hand the include the config's ABSOLUTE file:// URL
     so resolution never depends on ctx.baseUrl / can never fall back to cwd.
Both bins fixed identically. NOTE: the cordis Loader resolves a config's bare
plugin specifiers via its internal module loader, active only under
`node --expose-internals`; the bin cannot add a node flag itself, so this is
documented in the bin JSDoc + both package READMEs (the demos already comply).
The repo `examples/*/cordis.yml` are tsx-only artifacts (workspace plugins
resolve through the tsconfig paths map, not node_modules), so they are not a
valid plain-node bin target — the smokes use a real-install-shaped temp dir.

Fail loud on a load failure: boot() previously exited 0 SILENTLY when a config
path's directory does not exist — the include plugin fails to IMPORT, the cordis
Loader catches+LOGS it and leaves the entry with no fiber (no rejection), and
`loader.await()` does not rethrow (EntryTree.await uses Promise.allSettled). Fix:
boot() now calls assertEntriesLoaded(ctx) after the tree settles and throws on
any entry with no fiber, so a typo'd config dir exits non-zero with a clear
message. main() also installs an unhandledRejection guard (installFailLoud) that
replaces Node's stack dump with a single labelled stderr line for the
companion case (a missing config FILE in a real dir, whose include-init throw
surfaces as a rejection Node already exits non-zero on). Regression tests added
to both built-bin smokes (missing dir + missing file → non-zero exit + stderr);
verified the missing-dir test fails on the pre-fix bin.

Built-bin smokes (the reviewer's ask): packages/ui/{stdio,acp}-agent/tests/
built-bin.e2e.ts run the REAL lib/bin.js under `node` (NOT tsx) in a temp
consumer dir, asserting the stdio echo round-trip / the acp initialize response
+ stdout purity, plus the fail-loud cases above. They build-gate (skip if lib/
absent) and run in a new ci.yml step after the build.

Issue 2 — packages/README.md + docs/architecture.md said "plugins depend on
interfaces, never on the concrete loop", but dsh-agent-core imports the concrete
dsh-agent-loop. Scope the rule to EXTENSION plugins and carve out the sanctioned
COMPOSITION/bundle exception (dsh-agent-core composes the concrete spine); note
it in the implemented RFC too.

Issue 3 — examples/acp-agent/tests/acp.snapshot.ts fixture-guard claimed
no-model scenarios need no session.jsonl, but runScenario() always boots
llm-replay with the session.jsonl path and loadReplayScript() throws when it is
absent. Require session.jsonl for ALL scenarios (no-model ones ship a
header-only fixture) and rewrite the comment to match reality.

docs/rfc/implemented/architecture/2026-06-20-extract-example-app-packages.md

@@ -12,7 +12,7 @@ The deeper problem was a **coupled front-door cluster** that lived at the leaf w
 
 Each example is now **mostly an invocation of an app package**, splitting the wiring along the existing [interface / implementation / consumer seam](2026-06-13-capability-seams.md): the **app package owns the composition**, the leaf `cordis.yml` owns only the **swappable choices** (which LLM adapter, which bash executor, model, prompt, persistence root).
 
-- **`@deepseek-ai/dsh-agent-core`** ([packages/core/agent-core](../../../../packages/core/agent-core)) — a Cordis bundle plugin for the providerless, executor-less, UI-less spine: `timer` + `llm` + sessions + system-prompt + tools + agents + invariants + `tool-bash` + `agent-loop`, mounted as child plugins inside its `apply(ctx)` via `ctx.plugin(...)`. This is the old `base-core.yml` **minus** `bash-local`, **plus** `timer` and the loop, as code instead of a YAML include. The bundle **forwards** `agent-loop`'s `agents` list as its own config (`export const Config = AgentLoop.Config`, default `[]`, the existing `AgentLoop.Config` shape in [packages/core/agent-loop/src/index.ts](../../../../packages/core/agent-loop/src/index.ts)) — so each app supplies its own pre-created agents. This is precisely the reason the old `base-core.yml` gave for keeping `agent-loop` *out* of the shared core ("the examples disagree — stdio needs a pre-created `main`, acp needs none"); forwarding the config dissolves that objection — the loop is shared, the agents list is per-app. The bundle children register into the root service store, so a leaf-mounted sibling (the adapter, the executor) sees them exactly as a nested `plugin-include` subtree's services were seen before.
+- **`@deepseek-ai/dsh-agent-core`** ([packages/core/agent-core](../../../../packages/core/agent-core)) — a Cordis bundle plugin for the providerless, executor-less, UI-less spine: `timer` + `llm` + sessions + system-prompt + tools + agents + invariants + `tool-bash` + `agent-loop`, mounted as child plugins inside its `apply(ctx)` via `ctx.plugin(...)`. This is the old `base-core.yml` **minus** `bash-local`, **plus** `timer` and the loop, as code instead of a YAML include. The bundle **forwards** `agent-loop`'s `agents` list as its own config (`export const Config = AgentLoop.Config`, default `[]`, the existing `AgentLoop.Config` shape in [packages/core/agent-loop/src/index.ts](../../../../packages/core/agent-loop/src/index.ts)) — so each app supplies its own pre-created agents. This is precisely the reason the old `base-core.yml` gave for keeping `agent-loop` *out* of the shared core ("the examples disagree — stdio needs a pre-created `main`, acp needs none"); forwarding the config dissolves that objection — the loop is shared, the agents list is per-app. The bundle children register into the root service store, so a leaf-mounted sibling (the adapter, the executor) sees them exactly as a nested `plugin-include` subtree's services were seen before. Depending on the CONCRETE `dsh-agent-loop` (not just the `dsh-agent` interface) is deliberate and is the sanctioned exception to the "extension plugins depend on interfaces, never on the concrete loop" rule (packages/README.md, docs/architecture.md § Layering): the rule constrains plugins that EXTEND the system, whereas this bundle's whole job is to COMPOSE the concrete spine. Swapping the loop means publishing a different bundle, not rewiring every extension.
 - **`@deepseek-ai/dsh-stdio-agent`** ([packages/ui/stdio-agent](../../../../packages/ui/stdio-agent)) and **`@deepseek-ai/dsh-acp-agent`** ([packages/ui/acp-agent](../../../../packages/ui/acp-agent)) — app packages, each consuming `dsh-agent-core` and **baking in its coupled front-door cluster**: stdio = `ui-stdio` + console logger + a pre-created `main`; acp = the `acp` bridge + JSONL persistence + **no stdout logger** + no pre-created agents. The leaf no longer carries the cluster, so it has no logger entry to copy wrong by default — the common stdout-purity mistake loses its foothold. (A leaf can still *add* a sibling logger entry — a package cannot forbid what a leaf author writes — so the rule "never add a stdout logger to an ACP leaf" stays documented at the leaf; what changed is that the default leaf has nothing to get wrong.) They land under the existing `ui` group alongside `acp`, so no new package group (and no `tsconfig`/`packages/README` group plumbing) was needed.
 - **`start.ts` is gone.** Each app package exposes a `bin` (`dsh-stdio-agent` / `dsh-acp-agent`); the `demo:*` scripts invoke it (e.g. `dsh-stdio-agent ./cordis.yml`). The Loader-boot tail, `.env` loading, snapshot-mode selection, and stdin-dispose lifecycle moved into that bin, owned by the app. The `bin.ts` files are coverage-excluded (a self-executing CLI entry, like the old `start.ts`) and driven by the keyless Loader-path tests.
 - **Each leaf `cordis.yml` collapses** to backends + config: the LLM adapter (`llm-deepseek` with apiKey/models, or `llm-replay`), the bash executor (`bash-local`), `hmr` for the stdio demos (see the amendment below), and one app entry carrying the app's config (model, system prompt, persistence root — surfaced as the app package's own `Config`, which routes each value to wherever the app wires it: stdio onto its pre-created agent, acp onto the bridge plugin).