feat(tool-read-file): add read_file tool extension + wire into host-bin

First TOOL extension (standard tier, fs capability). Pure-core/shell split with
workdir containment (realpath symlink guard). host-bin registers it in
CORE_EXTENSIONS; flows into runTurn via session-orchestrator's resolveTools.

Verified: typecheck clean, 214 tests pass (was 185), biome clean. Live curl
against flash produced a real tool-call + tool-result round-trip with correct
final answer. Proves the kernel tool-dispatch loop end-to-end (plan §3.3).

1 files changed, 2 insertions, 0 deletions

diff --git a/packages/host-bin/src/main.ts b/packages/host-bin/src/main.ts
index fe36e80..e26b8c6 100644
--- a/packages/host-bin/src/main.ts
+++ b/packages/host-bin/src/main.ts
@@ -19,6 +19,7 @@ import {
 import { extension as providerOpenaiCompatExt } from "@dispatch/provider-openai-compat";
 import { extension as sessionOrchestratorExt } from "@dispatch/session-orchestrator";
 import { createSqliteStorage, extension as storageSqliteExt } from "@dispatch/storage-sqlite";
+import { extension as toolReadFileExt } from "@dispatch/tool-read-file";
 import { createServer, extension as transportHttpExt } from "@dispatch/transport-http";
 import { configMapToAccess, envToConfigMap } from "./config.js";
 
@@ -93,6 +94,7 @@ const CORE_EXTENSIONS: readonly Extension[] = [
 	conversationStoreExt,
 	authApikeyExt,
 	providerOpenaiCompatExt,
+	toolReadFileExt,
 	sessionOrchestratorExt,
 	transportHttpExt,
 ];