[Bug] Subagents inherit session model without cost confirmation, causing unintended quota drain on limited-quota models

Bug Description
Fully attributed now — zero ambiguity. The 2,448 Fable subagent messages are in 16 files under this session's subagents/ directory, and those 16 agent IDs are exactly the deep-audit auditors I launched. The entire audit ran on Fable, then this session switched to Opus-4.8 for the doctor/this investigation. So your instinct was correct: a brief Fable window, but it contained a 16-way fan-out I spawned. Here's the complete, paste-ready package. --- Bug report evidence — Fable 5 usage spike Environment - Claude Code 2.1.223 (native install, macOS, EDT/-0400) - Limit reset: Tue Aug 4 2026, 4:00 PM EDT (2026-08-04T20:00:00Z) - Report generated from local transcripts in ~/.claude/projects/ The event - A 16-agent audit workflow launched from one session (fb9157a6-…) while the session model was claude-fable-5. - Subagents inherited the session model, so all 16 ran as Fable, in parallel. - Burst window: 2026-08-06T19:41:55Z → 20:00:19Z = 18 min 24 sec (3:41–4:00 PM EDT) - Attribution: 16 transcript files under fb9157a6-…/subagents/agent-*.jsonl, 2,448 assistant messages total. Post-reset usage by model (since 2026-08-04T20:00:00Z) ┌──────────┬──────────────────┬───────┬────────────┬──────────────┬────────┐ │ Model │ Kind │ Msgs │ cache_read │ cache_create │ output │ ├──────────┼──────────────────┼───────┼────────────┼──────────────┼────────┤ │ fable-5 │ subagent (the │ 2,448 │ 724.0M │ 29.7M │ 0.59M │ │ │ burst) │ │ │ │ │ ├──────────┼──────────────────┼───────┼────────────┼──────────────┼────────┤ │ fable-5 │ main (your │ 65 │ 4.1M │ 0.5M │ 0.49M │ │ │ typing) │ │ │ │ │ ├──────────┼──────────────────┼───────┼────────────┼──────────────┼────────┤ │ opus-5 │ main (your real │ 6,566 │ 2,430.9M │ 26.6M │ 6.93M │ │ │ 2-day workload) │ │ │ │ │ ├──────────┼──────────────────┼───────┼────────────┼──────────────┼────────┤ │ opus-5 │ subagent …
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