t3_thread_list returns an empty list for a projectId that does not exist #29175

What happened

t3_thread_list with a projectId that does not exist returns a successful, empty result instead of an error. An agent that passes a wrong id sees {"projectId":"<unknown id>","threads":[],"nextCursor":null,"total":0} and concludes that the project exists and simply has no threads.

In our case this happened right after t3_thread_launch had failed for the same unknown id with the generic "The operation could not be completed." (#29094). The agent called t3_thread_list to verify the target, got a clean empty list, and retried the launch six times before giving up and reporting a T3 bug to the user.

Diagnosis

listThreads in apps/server/src/mcp/OrchestratorMcpService.ts (v0.1.6, 2359643c; unchanged on main at d01b92c0) resolves the target with resolveProjectTarget(parent, input.projectId) and passes the id straight to threadManagement.listProjectThreads. Nothing checks that the project exists. The same file has requireProject, which other launch paths and t3_project_read use to return invalid_request with "Project … was not found."

Steps to reproduce

1. In any thread, have the agent call t3_thread_list with projectId set to a random UUID (or a mistyped real id) and limit: 5.
2. Read the tool result.

Expected: an invalid_request failure saying the project was not found, as t3_project_read returns.
Actual: success with threads: [] and total: 0.

Version

Desktop app 0.1.6 (2359643c), local server 0.1.6. Triage CLI 0.1.6.

Environment

macOS arm64 (Darwin 27.0.0), T3 Code desktop app against the local server, Claude Agent provider (claude-opus-5-5).

Evidence

Provider event log of the calling thread, 2026-11-02 07:47:41Z:


call:   mcp__t3-code__t3_thread_list {"projectId":"20b75d6f-f2cf-4ea1-99b3-3eb11969a3a9","titleContains":"gitleaks","limit":5}
result: {"projectId":"20b75d6f-f2cf-4ea1-99b3-3eb11969a3a9","currentThreadId":"thread:project:mcp%3A…","threads":[],"nextCursor":null,"total":0}


`projection_projects` has no row with that id. The real project the agent meant is `20b75d6f-2e40-4ac8-ad1a-5a2dac05e39d`; the tail came from a neighbouring project's id in an earlier `t3_project_list` result.

Related issues

#29094 (the launch tool hides "Project not found." behind a generic message). The two together left the agent with no way to learn that its project id was wrong.

Fix applied or workaround

Call t3_project_read or t3_project_list to check the id before listing or launching.

Filed by

Filed via t3 triage by Claude Fable 5.1 in Claude Code.