fix(hooks): attribute native activity to the registered ECC session

Verify review discussion4419348312 against actual native producer/importer behavior. Prefer the independently sanitized ECC_SESSION_ID for the ECC-owned metrics feed, retain payload then legacy fallback for standalone hooks, and leave sibling hooks unchanged.

Actual Node producer plus read-only cached native binary reproduces zero imported metrics before the fix and exactly one tool/file/log after repeated sessions/status commands. Four producer regression controls and normal/adversarial inherited-env suites pass22/22. Focused coverage96.47percent lines and91.47percent branches; parent independent source review passed.

scripts/hooks/session-activity-tracker.js

@@ -562,9 +562,8 @@ function summarizeOutput(toolOutput) {
 }
 
 function buildActivityRow(input, env = process.env) {
-  // Same env-var-reliance bug as the session id below: Claude Code doesn't
-  // set CLAUDE_HOOK_EVENT_NAME for hook subprocesses either. Real hook stdin
-  // payloads carry hook_event_name as a JSON field -- prefer that.
+  // Claude Code does not set CLAUDE_HOOK_EVENT_NAME for hook subprocesses.
+  // Real hook stdin payloads carry hook_event_name as a JSON field.
   const hookEvent = String(
     input?.hook_event_name || env.CLAUDE_HOOK_EVENT_NAME || ''
   ).trim();
@@ -573,15 +572,14 @@ function buildActivityRow(input, env = process.env) {
   }
 
   const toolName = String(input?.tool_name || '').trim();
-  // Claude Code does not set CLAUDE_SESSION_ID as an environment variable for
-  // hook subprocesses -- the session id is only available in the hook's own
-  // stdin JSON payload. Prefer that; keep the env vars as a fallback for any
-  // caller that does set them. Sanitized the same way as the sibling hooks
-  // (cost-tracker.js, ecc-context-monitor.js, ecc-metrics-bridge.js,
-  // gateguard-fact-force.js) that already use this exact fallback order.
+  // Native ECC workers set ECC_SESSION_ID to their registered session ID.
+  // This feed belongs to that ECC session, even when the harness payload
+  // carries a different conversation ID. Standalone hooks use their payload
+  // ID before the legacy Claude environment fallback. Sanitize each candidate
+  // separately so an invalid native ID cannot hide a usable payload ID.
   const sessionId =
-    sanitizeSessionId(input?.session_id) ||
     sanitizeSessionId(env.ECC_SESSION_ID) ||
+    sanitizeSessionId(input?.session_id) ||
     sanitizeSessionId(env.CLAUDE_SESSION_ID) ||
     '';
   if (!toolName || !sessionId) {

tests/hooks/session-activity-tracker.test.js

@@ -60,7 +60,11 @@ function runScript(input, envOverrides = {}, options = {}) {
     encoding: 'utf8',
     input: inputStr,
     timeout: 10000,
-    env: { ...process.env, ...ISOLATED_HOME_ENV, ...envOverrides },
+    env: {
+      ...process.env, ...ISOLATED_HOME_ENV,
+      ECC_SESSION_ID: '', CLAUDE_SESSION_ID: '',
+      ...envOverrides,
+    },
     cwd: options.cwd,
   });
   return { code: result.status || 0, stdout: result.stdout || '', stderr: result.stderr || '' };
@@ -414,6 +418,38 @@ function runTests() {
     fs.rmSync(tmpHome, { recursive: true, force: true });
   }) ? passed++ : failed++);
 
+  for (const [label, eccId, payloadId, legacyId, expectedId] of [
+    ['native ECC identity wins over the distinct harness payload', 'ecc-native-owner', 'claude-conversation', 'stale-parent', 'ecc-native-owner'],
+    ['standalone payload wins over a stale legacy environment', '', 'claude-standalone', 'stale-parent', 'claude-standalone'],
+    ['invalid ECC identity falls back to the payload', '../invalid-owner', 'claude-standalone', 'stale-parent', 'claude-standalone'],
+    ['invalid ECC and payload identities fall back to the legacy environment', 'bad/owner', 'bad\\payload', 'claude-legacy', 'claude-legacy'],
+  ]) {
+    (test(`actual activity producer: ${label}`, () => {
+      const tmpHome = makeTempDir();
+      try {
+        const input = {
+          hook_event_name: 'PostToolUse', session_id: payloadId,
+          tool_name: 'Read', tool_input: { file_path: 'src/identity.ts' },
+        };
+        const result = runScript(input, {
+          ...withTempHome(tmpHome),
+          ECC_AGENT_DATA_HOME: path.join(tmpHome, '.claude'),
+          CLAUDE_CONFIG_DIR: path.join(tmpHome, '.claude'),
+          ECC_SESSION_ID: eccId, CLAUDE_SESSION_ID: legacyId,
+        });
+        assert.strictEqual(result.code, 0, result.stderr);
+        assert.strictEqual(result.stdout, JSON.stringify(input));
+        const rows = readMetricRows(tmpHome);
+        assert.strictEqual(rows.length, 1);
+        assert.strictEqual(rows[0].session_id, expectedId);
+        assert.strictEqual(rows[0].tool_name, 'Read');
+        assert.deepStrictEqual(rows[0].file_paths, ['src/identity.ts']);
+      } finally {
+        fs.rmSync(tmpHome, { recursive: true, force: true });
+      }
+    }) ? passed++ : failed++);
+  }
+
   (test('reads session_id from stdin JSON when no session env var is set', () => {
     // Claude Code does not set CLAUDE_SESSION_ID for hook subprocesses in
     // real invocations -- the session id only arrives via stdin JSON.