Harden diagnostic response redaction

Redact every diagnostic response at the agent boundary, fail closed when sanitization cannot complete, and remove Windows, UNC, and slash-UNC paths from returned data. Preserve benign text while removing complete configured secret values, including nested JSON escapes and quoted HTML credential fields. Add focused regression coverage for collector errors, successful responses, support bundles, path variants, and punctuation secrets.

tests/diagnostics-agent.test.js

@@ -1,6 +1,7 @@
 const { test } = require('node:test');
 const assert = require('node:assert');
 const { createAgent } = require('../lib/diagnostics-agent');
+const { valueScrub } = require('../lib/support-bundle');
 
 function stubCollectors() {
   const calls = [];
@@ -28,6 +29,9 @@ test('agent rejects unknown ops and any write/exec-shaped op', () => {
     assert.equal(r.ok, false, `${bad} must be rejected`);
     assert.match(r.error, /unknown or non-readonly/);
   }
+  const pathShaped = agent.handle('C:\\Users\\PrivateProfile\\operation', {});
+  assert.ok(!pathShaped.error.includes('PrivateProfile'));
+  assert.match(pathShaped.error, /<redacted-path>/);
 });
 
 test('agent rejects inherited Object.prototype members (no whitelist bypass via the prototype chain)', () => {
@@ -53,10 +57,43 @@ test('agent maps each whitelisted op to its collector and is read-only only', ()
   for (const op of agent.ops) assert.ok(!/write|delete|set_|exec|restart|cancel|retry/.test(op), `${op} must be read-only`);
 });
 
-test('agent surfaces a collector ok:false verbatim and never throws', () => {
-  const agent = createAgent({ readLog: () => ({ ok: false, error: 'unknown or non-readable log: x' }), getSystemInfo: () => { throw new Error('boom'); } });
+test('agent redacts collector failures and thrown errors at the response boundary', () => {
+  const drivePath = 'C:\\Users\\PrivateProfile\\secret.log';
+  const uncPath = '\\\\?\\UNC\\private-server\\secret-share\\secret.log';
+  const agent = createAgent({
+    readLog: () => ({ ok: false, error: `cannot read ${drivePath}` }),
+    getSystemInfo: () => { throw new Error(`boom at ${uncPath}`); }
+  });
   assert.equal(agent.handle('read_log', { name: 'x' }).ok, false);
+  assert.ok(!JSON.stringify(agent.handle('read_log', { name: 'x' })).includes('PrivateProfile'));
   const thrown = agent.handle('get_system_info', {});
   assert.equal(thrown.ok, false);
   assert.match(thrown.error, /boom/);
+  assert.ok(!thrown.error.includes('private-server'));
+  assert.match(thrown.error, /<redacted-path>/);
+});
+
+test('agent redacts every successful response with configured secrets at the boundary', () => {
+  const secret = 'configured-secret-123';
+  const slashUnc = '//private-server/secret-share/secret.log';
+  const collectors = stubCollectors();
+  collectors.getSystemInfo = () => ({ nested: { message: `token ${secret}`, path: slashUnc } });
+  collectors.redactResponse = value => valueScrub(value, [secret]);
+  const result = createAgent(collectors).handle('get_system_info', {});
+  const json = JSON.stringify(result);
+  assert.equal(result.ok, true);
+  assert.ok(!json.includes(secret));
+  assert.ok(!json.includes('private-server'));
+  assert.match(json, /<redacted>/);
+  assert.match(json, /<redacted-path>/);
+});
+
+test('agent fails closed when response redaction fails', () => {
+  const agent = createAgent({
+    getSystemInfo: () => ({ token: 'must-not-leak' }),
+    redactResponse: () => { throw new Error('redactor unavailable'); }
+  });
+  const result = agent.handle('get_system_info', {});
+  assert.deepEqual(result, { ok: false, error: 'diagnostic response could not be safely returned' });
+  assert.ok(!JSON.stringify(result).includes('must-not-leak'));
 });