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/src/agent.ts

@@ -1,3 +1,11 @@
+/**
+ * The concrete Agent implementation: LoopAgent plus its inbox. Everything
+ * observable happens through session events and the agent/* event taxonomy —
+ * plugins never need this class.
+ *
+ * @module dsh-agent-loop/agent
+ */
+
 import type { Context } from 'cordis'
 import type { AgentOptions, AgentStatus, SendOptions } from '@deepseek-ai/dsh-agent'
 import type { Agent } from '@deepseek-ai/dsh-agent'
@@ -72,7 +80,12 @@ export class LoopAgent implements Agent {
     this.currentAbort?.abort(reason ?? 'aborted')
   }
 
-  /** Start the driver loop. Returns a disposer that stops it. */
+  /**
+   * Start the driver loop. Returns a disposer: calling it sets status to
+   * `disposed`, emits `agent/status('disposed')`, resolves the disposed
+   * promise (unblocking the idle wait), and aborts the current request if
+   * any. The returned `agent.done` promise resolves once the loop exits.
+   */
   start(): () => void {
     this.done = runLoop(this.ctx, this, {
       setStatus: status => this.setStatus(status),