security(crypto): replace SHA-1 with SHA-256 in all hash operations

SHA-1 is cryptographically broken and vulnerable to collision
attacks. Replace all internal usages with SHA-256:

- sandbox session key slugs (shared.ts)
- sandbox config change detection (config-hash.ts)
- tool call ID generation (tool-call-id.ts)
- gateway lock file naming (gateway-lock.ts)

All hashes are ephemeral (session-scoped slugs, lock filenames,
tool IDs) so the algorithm change has no persistence impact.

Fixes #2994

src/agents/sandbox/config-hash.ts

@@ -49,5 +49,5 @@ function primitiveToString(value: unknown): string {
 export function computeSandboxConfigHash(input: SandboxHashInput): string {
   const payload = normalizeForHash(input);
   const raw = JSON.stringify(payload);
-  return crypto.createHash("sha1").update(raw).digest("hex");
+  return crypto.createHash("sha256").update(raw).digest("hex");
 }

src/agents/sandbox/shared.ts

@@ -7,7 +7,7 @@ import { resolveAgentIdFromSessionKey } from "../agent-scope.js";
 
 export function slugifySessionKey(value: string) {
   const trimmed = value.trim() || "session";
-  const hash = crypto.createHash("sha1").update(trimmed).digest("hex").slice(0, 8);
+  const hash = crypto.createHash("sha256").update(trimmed).digest("hex").slice(0, 8);
   const safe = trimmed
     .toLowerCase()
     .replace(/[^a-z0-9._-]+/g, "-")

src/agents/tool-call-id.ts

@@ -40,7 +40,7 @@ export function isValidCloudCodeAssistToolId(id: string, mode: ToolCallIdMode =
 }
 
 function shortHash(text: string, length = 8): string {
-  return createHash("sha1").update(text).digest("hex").slice(0, length);
+  return createHash("sha256").update(text).digest("hex").slice(0, length);
 }
 
 function makeUniqueToolId(params: { id: string; used: Set<string>; mode: ToolCallIdMode }): string {

src/infra/gateway-lock.test.ts

@@ -29,7 +29,7 @@ async function makeEnv() {
 function resolveLockPath(env: NodeJS.ProcessEnv) {
   const stateDir = resolveStateDir(env);
   const configPath = resolveConfigPath(env, stateDir);
-  const hash = createHash("sha1").update(configPath).digest("hex").slice(0, 8);
+  const hash = createHash("sha256").update(configPath).digest("hex").slice(0, 8);
   const lockDir = resolveGatewayLockDir();
   return { lockPath: path.join(lockDir, `gateway.${hash}.lock`), configPath };
 }

src/infra/gateway-lock.ts

@@ -150,7 +150,7 @@ async function readLockPayload(lockPath: string): Promise<LockPayload | null> {
 function resolveGatewayLockPath(env: NodeJS.ProcessEnv) {
   const stateDir = resolveStateDir(env);
   const configPath = resolveConfigPath(env, stateDir);
-  const hash = createHash("sha1").update(configPath).digest("hex").slice(0, 8);
+  const hash = createHash("sha256").update(configPath).digest("hex").slice(0, 8);
   const lockDir = resolveGatewayLockDir();
   const lockPath = path.join(lockDir, `gateway.${hash}.lock`);
   return { lockPath, configPath };