Repository navigation
[Bug]: Claude Code threads get T3 instructions meant for other agents #16465
Description
Before submitting
- I searched existing issues and did not find a duplicate.
- I included enough detail to reproduce or investigate the problem.
Area
apps/server
Steps to reproduce
- Run T3 Code 0.0.46-nightly.20261005.2702 and open any project.
- Start a new thread with Claude Code (Full access).
- Send: "Quote, word for word, the section of your system prompt titled "T3 Code orchestration", including any paragraph about an ACP fallback and any example tool name with an "mcp__" prefix. Do not summarize. Then tell me the exact names of the T3 tools you have, as you would call them."
Expected behavior
Claude Code only gets instructions that apply to Claude Code, the way Codex already gets its own version (CodexDeveloperInstructions.ts).
Actual behavior
Claude quotes two things that don't apply to it:
- The "ACP fallback" paragraph, which tells the agent to call T3 tools through the terminal with
T3_ACP_MCP_NODEandacp-mcp-call. Claude Code never uses this path. It's about 166 tokens in every Claude thread. - The example tool name
mcp__t3_code__delegate_task, with an underscore. In Claude Code, T3's tools are namedmcp__t3-code__…, with a dash. Claude said so itself: "My actual tools usemcp__t3-code__with a hyphen, somcp__t3_code__delegate_taskwould not match anything here."
It then listed its 75 T3 tools, all starting with mcp__t3-code__.
Likely cause: apps/server/src/provider/T3OrchestrationInstructions.ts is one shared text for every agent, and apps/server/src/orchestration-v2/Adapters/ClaudeAdapterV2.ts adds all of it to Claude's system prompt whenever the t3-code MCP server is attached.
Impact
Minor bug or occasional failure
Version or commit
0.0.46-nightly.20261005.2702 (cfa4f76)
Environment
macOS 15 (Darwin 24.6), T3 run with t3 serve, Claude Code 2.1.288
Logs or stack traces
Screenshots, recordings, or supporting files
No response
Workaround
None needed. Claude mostly ignores it, but it costs tokens in every thread and the wrong tool name can mislead.
Activity
juliusmarminge commentedon Oct 6, 2026
Note
Grok responding on behalf of Julius.
Triage
Thanks @slkiser for the clean repro prompt and for pointing straight at the right files. Reading current
main, this is still the case aftercfa4f765.What I found
T3_CODE_ORCHESTRATION_INSTRUCTIONSis one shared string, andmakeClaudeQueryOptionsappends all of it to Claude Code's system prompt whenever thet3-codeMCP server is attached. Two parts don't apply to Claude:T3_ACP_MCP_NODE,acp-mcp-call). That environment variable is only set for ACP sessions, and the paragraph only applies when the T3 tools are absent from the turn, so for Claude it's extra tokens rather than a path it's meant to take.tools.mcp__t3_code__orchestrator_capabilities({})) and the sample namemcp__t3_code__delegate_task. Claude registers these tools asmcp__t3-code__…(hyphen), which is also whatCLAUDE_T3_MCP_TOOL_WILDCARDand the read-only allowlist use.CodexDeveloperInstructions.tsonly builds the Plan/Default collaboration-mode instructions, and Codex still receives the same shared orchestration string (ACP fallback included) throughbuildCodexAdditionalContext. Cursor, OpenCode, and Pi inject the same string too.Likely fix area
apps/server/src/provider/T3OrchestrationInstructions.tsand the per-adapter injection points. One option is to keep the shared guidance (delegate vs. top-level threads, schedules, secrets, worktrees, HTML preview) shared, add the ACP fallback only for ACP harnesses and the code-mode example only for Codex, and usemcp__t3-code__for any concrete tool-name example shown to Claude.A maintainer will decide on the fix direction.