[Bug]: Plan sidebar stays empty on Claude 5 models — Claude Code no longer exposes the Task tools by default

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Assessment

Difficulty
1/5
Estimated time
Under an hour
Newbie friendliness
86/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Active
Tech stack
typescript
Domain
backend

Research direction

Start in apps/server and locate makeClaudeEnvironment, then inspect how Claude session environment variables are assembled. Set CLAUDE_CODE_ENABLE_TODO_TOOLS=1 and reproduce a Claude 5 session with multi-step work. Done means Task tools appear in the init event and updates populate the existing plan sidebar without client changes.

Written by the indexing model from the issue text.

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
  1. Start a new thread on the Claude provider with a Claude 5 family model (Fable 5, Sonnet 5, Opus 5; bundled Claude Code 2.1.252).
  2. Ask for multi-step work and request progress tracking with tasks.
  3. Watch the plan sidebar.
Expected behavior

Task updates stream into the plan sidebar, as they did after #1541 and as Codex plan steps do.

Actual behavior

The sidebar never populates. The session's init event lists no TaskCreate/TaskUpdate/TaskList tools, so the server's mapping to turn.plan.updated has nothing to consume.

Per Anthropic's docs (https://code.claude.com/docs/en/agent-sdk/todo-tracking#model-availability), Agent SDK 0.3.233+ leaves the task-tracking tools out of sessions on Opus 4.8, Sonnet 5, Fable 5, and Mythos 5 unless the embedding application opts in. TodoWrite is gone in the same versions, so both branches of the #1541 mapping are dead for Claude 5 sessions. Haiku 4.5 sessions still get the tools, confirming the model gate. The docs direct applications that render these tool calls to set CLAUDE_CODE_ENABLE_TODO_TOOLS=1.

Suggested fix

Set CLAUDE_CODE_ENABLE_TODO_TOOLS=1 in the Claude session environment (makeClaudeEnvironment). Verified locally against the bundled binary: with the variable set (via env or a Claude settings.json env map), a Fable 5 session exposes TaskCreate/TaskGet/TaskList/TaskUpdate and the sidebar populates again through the existing mapping, with no client changes.

Dominant language
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