[Bug] Usage attribution overstates skills with handoffs and inconsistent subagent handling

Bug Description
Usage-by-skill attribution overstates skills that hand off to work, and is inconsistent
around subagents

Version: Claude Code 2.1.280, macOS arm64

What I see
The usage command charges a lot of usage to my "backlog" skill. The session transcripts
show why: each assistant API call carries an attributionSkill field, and the stamp is
applied like this:

• It starts on the first call after a Skill tool call. Calls earlier in the turn, and the

call that requested the skill, are not stamped.

• It stays on every later call in the turn until the next user prompt.
• A later Skill call in the same turn replaces it.
• A subagent spawned while it is active inherits it for its whole run, even though the

subagent never calls Skill itself.

• When a background subagent's report comes back to the main thread, the stamp clears

mid-turn.

Why it matters

1. A skill's attribution has no end. My "backlog pick" skill picks an item and sets up a

worktree in a few calls, then the implementation continues in the same turn (tens of
calls) and is all charged to the skill. Across 40 recent sessions, "backlog" was about
11% of main-thread tokens, and most of that was not the skill's own work. So the
breakdown can't answer "which skills are expensive to run".

1. The subagent handling is inconsistent. Spawning a subagent extends the stamp: 14

subagent transcripts were stamped for their whole run, 16-31 calls each. The same
subagent's report coming back ends the stamp on the main thread. Both events belong to
the same delegation, but they have opposite effects.

Repro

1. Invoke a skill, then keep working in the same turn (edits, Bash).
2. Spawn a subagent (Agent tool) in that same turn and let it return.
3. Compare attributionSkill in the session .jsonl with the one in

<session>/subagents/*.jsonl.

Expected
Either attribution that follows what the skill itself did (for example ending when the
skill's own work ends, or giving the user a way to mark that), or documented rules, with
subagents and their returns handled the same way.

Environment Info

• Platform: darwin
• Terminal: vscode
• Version: 2.1.280
• Feedback ID: 1f9a310e-6cbb-47d5-9291-b2e9686b56a4