[barelyworkingcode]

Closes #592

Child of #596 (session adoption, eve track). Targets epic/596-session-adoption.

An idle headless Claude agent now shows Drop in on Today, the project page and the Chief of Staff rail and sheet. A working one shows Take over after this turn: the same POST, which relay holds until the turn ends. A refusal shows relay's reason in a one-line toast. This page never offers Take over on a session its own drop-in terminal holds. Outside rows never get either button.

Decisions:

• The phone sheet stays open with the waiting text, and closes when relay answers (contract question 2).
• "With its history" and relay's real turn wait are left to the epic's real-app check. The pinned fakerelay drop-in is an echo terminal and cannot hold a Claude turn (contract questions 3 and 4).
• No relay change, no pin bump, no devboxverify journey change (contract question 5).

Fix attempts: product code none after the first commit. The spec took four rounds: a missing claude-code template and loose locators, then three review findings on waits that could not fail. Tokens: about 0.5M across subagents.

Minor/theoretical (not changed): if onAnswer or openDropIn threw after a 201, dropIn would toast a second time; a relay answer closes a sheet reopened during the wait. Neither throws or misbehaves today.

Review: no blocking findings (round 3, after two rounds of spec fixes)
Journey: n/a: no devboxverify journey change; g6-drop-in.spec.js drives the idle and Take over paths, and agent-drop-in stays G6.23's devbox journey
Break-and-restore: removing the idle branch of showsDropIn turned 16 of 19 red; un-collapsing the toast and making busy text follow the group each turned their test red; all restored byte for byte

🤖 Generated with Claude Code

[barelyworkingcode]

merge-check: merged. approved, target, contract, evidence, owner, weakening

[barelyworkingcode]

Merged by merge-check: approved, target, contract, evidence, owner, weakening PASS; ci and verified NA (epic child).