fix: hide injected timestamp prefixes in chat ui

src/auto-reply/reply/strip-inbound-meta.test.ts

@@ -120,6 +120,32 @@ Hello from user`;
   });
 });
 
+describe("timestamp prefix stripping", () => {
+  it("strips a leading injected timestamp prefix", () => {
+    expect(stripInboundMetadata("[Wed 2026-03-11 23:51 PDT] hello")).toBe("hello");
+  });
+
+  it("strips timestamp prefix with UTC timezone", () => {
+    expect(stripInboundMetadata("[Thu 2026-03-12 07:00 UTC] what time is it?")).toBe(
+      "what time is it?",
+    );
+  });
+
+  it("leaves non timestamp brackets alone", () => {
+    expect(stripInboundMetadata("[some note] hello")).toBe("[some note] hello");
+  });
+
+  it("strips timestamp prefix and inbound metadata blocks together", () => {
+    const input = `[Wed 2026-03-11 23:51 PDT] Conversation info (untrusted metadata):
+\`\`\`json
+{"message_id":"msg-1","sender":"+1555"}
+\`\`\`
+
+Hello`;
+    expect(stripInboundMetadata(input)).toBe("Hello");
+  });
+});
+
 describe("extractInboundSenderLabel", () => {
   it("returns the sender label block when present", () => {
     const input = `${CONV_BLOCK}\n\n${SENDER_BLOCK}\n\nHello from user`;

src/auto-reply/reply/strip-inbound-meta.ts

@@ -7,8 +7,13 @@
  * etc.) directly to the stored user message content so the LLM can access
  * them. These blocks are AI-facing only and must never surface in user-visible
  * chat history.
+ *
+ * Also strips the timestamp prefix injected by `injectTimestamp` so UI surfaces
+ * do not show AI-facing envelope metadata as user text.
  */
 
+const LEADING_TIMESTAMP_PREFIX_RE = /^\[[A-Za-z]{3} \d{4}-\d{2}-\d{2} \d{2}:\d{2}[^\]]*\] */;
+
 /**
  * Sentinel strings that identify the start of an injected metadata block.
  * Must stay in sync with `buildInboundUserContextPrefix` in `inbound-meta.ts`.
@@ -121,11 +126,16 @@ function stripTrailingUntrustedContextSuffix(lines: string[]): string[] {
  * (fast path — zero allocation).
  */
 export function stripInboundMetadata(text: string): string {
-  if (!text || !SENTINEL_FAST_RE.test(text)) {
+  if (!text) {
     return text;
   }
 
-  const lines = text.split("\n");
+  const withoutTimestamp = text.replace(LEADING_TIMESTAMP_PREFIX_RE, "");
+  if (!SENTINEL_FAST_RE.test(withoutTimestamp)) {
+    return withoutTimestamp;
+  }
+
+  const lines = withoutTimestamp.split("\n");
   const result: string[] = [];
   let inMetaBlock = false;
   let inFencedJson = false;