fix(mcp): handle 400 auth errors, clear auth mode after OAuth, trim tokens (#1158)

* fix(mcp): handle 400 auth errors, clear auth mode after OAuth, trim tokens

Three bugs prevented MCP server authentication (e.g. GitHub MCP) from
working correctly:

1. **400 treated as auth-required**: GitHub's MCP endpoint returns 400
   "Authorization header is badly formatted" instead of 401 when auth
   is missing. Broadened auth detection in activate_mcp, send_request,
   and discover_via_401 to also match 400+authorization errors.

2. **Auth mode not cleared after OAuth callback**: The OAuth callback
   handler and setup submit handler did not call clear_auth_mode(),
   leaving pending_auth on the thread. The next user message was
   intercepted as a token instead of triggering an LLM turn.

3. **Token trimming**: Tokens with leading/trailing whitespace or
   newlines produced malformed Authorization headers. Now trimmed
   before storage (configure) and before use (build_request_headers).

Adds E2E tests with a mock MCP server (JSON-RPC + OAuth discovery +
DCR + token exchange) covering install -> activate -> OAuth callback ->
LLM turn lifecycle, plus a GitHub-style 400 error variant.

[skip-regression-check]

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>

* fix(mcp): add TTL to PendingAuth and clear auth mode on all failure paths

Auth mode (pending_auth on a Thread) had no timeout and several code
paths that failed to clear it, causing user messages to be swallowed
indefinitely. This adds defense-in-depth:

- Add created_at + 5-minute TTL to PendingAuth; auto-clear on next
  message if expired (safety net for edge cases like user closing
  browser mid-OAuth)
- Clear auth mode on OAuth callback failure paths (unknown/consumed
  state, expired flow)
- Move clear_auth_mode before configure() match in setup_submit so
  it runs on failure too (addresses Copilot review feedback)

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>

* fix(ci): exclude test hunks from unwrap/assert pre-commit check

The pre-commit safety script only excluded files in tests/ but not
#[cfg(test)] mod tests blocks inside src/ files. Use the git diff @@
hunk header context (which includes the enclosing function name) to
detect and skip test hunks.

Also removes unnecessary // safety: comments from test assertions.

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>

* fix: restore formatting in test assertions

The replace_all edit that removed // safety: comments collapsed
newlines. Restore proper line breaks.

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>

* fix: address Copilot review - tighten pre-commit filter, document TTL sync

- pre-commit-safety.sh: only exclude `mod tests` hunks (not `fn test_*`)
  to avoid hiding unwrap/assert in production functions like test_server()
- session.rs: extract AUTH_MODE_TTL_SECS constant and add doc comment
  linking to OAUTH_FLOW_EXPIRY to prevent silent drift

[skip-regression-check]

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>

* fix(mcp): return error on expired auth input, clear auth on all OAuth paths

- When auth mode TTL expires and the user sends a message (possibly a
  pasted token), return an explicit "expired, please retry" response
  instead of forwarding the content to the LLM/history
- Add clear_auth_mode() to all early-return paths in oauth_callback_handler
  (provider error, missing state/code, no extension manager)

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>

---------

Co-authored-by: Claude Opus 4.6 (1M context) <[email protected]>

src/agent/agent_loop.rs

@@ -838,19 +838,42 @@ impl Agent {
         };
 
         if let Some(pending) = pending_auth {
-            match &submission {
-                Submission::UserInput { content } => {
-                    return self
-                        .process_auth_token(message, &pending, content, session, thread_id)
-                        .await;
-                }
-                _ => {
-                    // Any control submission (interrupt, undo, etc.) cancels auth mode
+            if pending.is_expired() {
+                // TTL exceeded — clear stale auth mode
+                tracing::warn!(
+                    extension = %pending.extension_name,
+                    "Auth mode expired after TTL, clearing"
+                );
+                {
                     let mut sess = session.lock().await;
                     if let Some(thread) = sess.threads.get_mut(&thread_id) {
                         thread.pending_auth = None;
                     }
-                    // Fall through to normal handling
+                }
+                // If this was a user message (possibly a pasted token), return an
+                // explicit error instead of forwarding it to the LLM/history.
+                if matches!(submission, Submission::UserInput { .. }) {
+                    return Ok(Some(format!(
+                        "Authentication for **{}** expired. Please try again.",
+                        pending.extension_name
+                    )));
+                }
+                // Control submissions (interrupt, undo, etc.) fall through to normal handling
+            } else {
+                match &submission {
+                    Submission::UserInput { content } => {
+                        return self
+                            .process_auth_token(message, &pending, content, session, thread_id)
+                            .await;
+                    }
+                    _ => {
+                        // Any control submission (interrupt, undo, etc.) cancels auth mode
+                        let mut sess = session.lock().await;
+                        if let Some(thread) = sess.threads.get_mut(&thread_id) {
+                            thread.pending_auth = None;
+                        }
+                        // Fall through to normal handling
+                    }
                 }
             }
         }