Document the codebase thoroughly and tighten type safety

Docs: per-folder README.md for packages/ (family overview + one per
package: service, events, API, extension points, TODOs), examples/,
and examples/echo-agent/; folder-level AGENTS.md (+ CLAUDE.md
symlinks) for packages/ and vendor/; module-level doc comments in
every packages/*/src file; richer JSDoc on all exported API
(event side effects, disposal contracts, error behavior). Root
AGENTS.md gains a "Type Safety and Documentation" policy section:
the codebase aims to be very type-safe and well documented; type
gymnastics are acceptable in core packages when they improve
plugin-author DX; verbose docs are fine as long as they stay strictly
in sync with the code.

Type safety: removed the upstream-inherited "noImplicitAny": false
from tsconfig.base.json — packages/* now compile under full strict
mode; vendor/loader and vendor/include set it locally (vendor/cordis
already did). Eliminated every `: any` / `as any` from packages and
examples (catch clauses use unknown + a CodedError narrowing type;
event data access uses discriminated-union narrowing).

Typed tool schemas: new @deepseek-ai/dsh-tools schema DSL —
SchemaSpec with per-property `required: true` booleans, type-level
InferArgs<S>, a runtime SchemaSpec → JSON Schema converter, and
defineTool() so first-party tools get typed execute(args) with zero
casts (raw JSON Schema still accepted for MCP interop; chosen over
schemastery because it targets JSON Schema generation directly).
echo-tool and all test tools migrated; +7 tests.

packages/agent-loop/README.md

@@ -0,0 +1,83 @@
+# dsh-agent-loop
+
+THE concrete agent plugin: `LoopAgent` and the loop driver. Implements the
+`Agent` interface and drives the session/turn/step lifecycle.
+
+This is the only package in the harness that contains concrete loop logic.
+Everything else is an abstract service or a plugin against extension seams —
+new behavior goes into plugins, not here.
+
+## Service: `AgentLoop` (ctx key: `agentLoop`)
+
+### Public API
+
+- `ctx.agentLoop.create(id: string, options?: AgentOptions): LoopAgent`
+  Create an agent, start its loop, and register it in `ctx.agents`. Disposed
+  with the calling fiber.
+
+### Injected services
+
+`agents`, `sessions`, `llm`, `tools`, `systemPrompt` — all five interface
+services.
+
+### Configuration (schemastery)
+
+```ts
+Config: {
+  agents: Array<{
+    id: string                 // required
+    model?: string
+    systemPrompt?: string
+  }>
+}
+```
+
+Agents listed in config are auto-created at startup.
+
+### Classes
+
+- `LoopAgent` — the concrete `Agent` implementation. Owns the inbox (`Inbox`),
+  the per-step `AbortController`, and the loop driver. Everything observable
+  happens through session events and the `agent/*` event taxonomy.
+- `Inbox` — per-agent queued + steering FIFOs (`enqueue`, `steer`, `drainQueued`,
+  `drainSteering`, `waitForQueued`).
+
+### Loop lifecycle (`loop.ts`)
+
+One invocation of `runLoop()` drives one agent for its whole lifetime:
+
+```
+forever:
+  wait for queued messages (idle)
+  TURN (error-contained):
+    drain queued → session('user/message') → 'turn/start'
+    STEP loop:
+      drain steering
+      assembly = systemPrompt.assemble()
+      request = waterfall agent/request
+      stream llm.stream(request) → session('assistant/chunk')
+      message = waterfall agent/step-result
+      session('assistant/message')
+      each tool-call: session('tool/call') → tools.execute() → session('tool/result')
+      drain steering → session('steering/message')
+      cont = waterfall agent/turn-continuation
+      if !cont: break
+    session('turn/end')
+    await session/flush
+    re-enqueue leftover steering as queued
+  idle unless more queued
+```
+
+Error containment: a throwing plugin ends the **turn**, never the loop. Dispose
+mid-turn emits `agent/status('disposed')` and ends with reason `disposed`.
+
+### What is NOT here
+
+Everything that goes beyond "call the model, run the tools, repeat" belongs to
+plugins listening on the event taxonomy:
+- Hooks: `agent/request`, `agent/step-result`, `tools/execute`, `agent/turn-continuation`
+- Compaction: `agent/request`
+- Sandbox, permission, plan mode: `tools/execute`
+- Sub-agents: TODO seam on `AgentLoop.create()`
+- Persistence: `session/event` + `session/flush`
+- UI: `agent/stream-chunk` + `agent/*` events