Implement the agent loop plugin

@deepseek-ai/dsh-agent-loop: LoopAgent (inbox with queued + steering
FIFOs, per-step AbortController) and the streaming-first
session/turn/step loop. Extension seams: agent/request,
agent/step-result, agent/turn-continuation waterfalls; raw chunks
logged for replay while BlockAssembler builds the assembled message;
steering drains between steps; session/flush awaited at turn end.

16 tests with a scripted mock adapter cover turn lifecycle ordering,
tool round-trips, steering, inject(), continuation override/veto,
mid-stream abort, queued turn chaining, replay equivalence, and
mid-turn fiber disposal (HMR safety).

packages/agent-loop/tsconfig.json

@@ -0,0 +1,18 @@
+{
+  "extends": "../../tsconfig.base.json",
+  "compilerOptions": {
+    "rootDir": "src",
+    "outDir": "lib"
+  },
+  "include": ["src"],
+  "references": [
+    { "path": "../../vendor/cosmokit" },
+    { "path": "../../vendor/cordis" },
+    { "path": "../../vendor/schemastery" },
+    { "path": "../llm" },
+    { "path": "../session" },
+    { "path": "../system-prompt" },
+    { "path": "../tools" },
+    { "path": "../agent" }
+  ]
+}