[BUG] Max 20x: Fable 5.1 refused and billed to usage credits once the general weekly limit is hit, while the separate Fable weekly bucket shows ~90% unused

Bug Description
On Max 20x, once the general weekly limit ("This week, all models") reaches 100%, Fable 5.1 is refused everywhere even though the separate "Fable this week" bucket shows most of its allowance unused (6% used at the first refusal, about 10% used at the second). With usage credits on, every Fable 5.1 call then bills usage credits. With usage credits off, Fable 5.1 is refused in both Claude Code and claude.ai. The Fable bucket therefore cannot be used at all once the general bucket is empty, which contradicts the usage screen that shows it as a separate weekly limit.

Observed, 2026-10-06 (America/Los_Angeles)

• 06:40 PDT: claude.ai usage screen: "Limit hit. You can send new messages when your week resets Friday, 11:00 PM PDT." Current session 10% used; This week 100% used; Fable this week 6% used ("Separate weekly limit for Fable").
• 06:44 to 06:45 PDT: a Claude Code background session started with --model claude-opus-5-5, plus 3 subagents, stopped with "You've hit your weekly limit · resets Oct 9 at 11pm (America/Los_Angeles)". Expected for Opus.
• 06:46 PDT: the session was switched to Fable 5.1 (/model claude-fable-5-1) and resumed; usage credits were turned on. Its subagents ran on claude-fable-5-1 (confirmed in the transcripts' "model" fields). Usage credits were consumed continuously.
• 06:58 to 07:02 PDT: two fresh background sessions started with claude --bg --model claude-fable-5-1 (every assistant turn in their transcripts is claude-fable-5-1; a guard script checked every transcript for any other model and found none). Both still got "You've hit your weekly limit · resets Oct 9 at 11pm" repeatedly, and credits kept being consumed between the refusals. Fable bucket at about 10% at that time.
• With usage credits turned off, Fable 5.1 was refused in claude.ai chat too (same weekly-limit message), with the Fable bucket still showing about 90% unused.

Expected
Fable 5.1 requests draw from the Fable weekly bucket while it has allowance left, in Claude Code and in claude.ai, regardless of the general bucket; usage credits are charged only once the Fable bucket is also exhausted (or not at all with credits off, with a refusal that names the Fable bucket).

Environment

• Claude Code 2.1.274 (and 2.1.291 earlier the same day), macOS 26.6.2, Max 20x, login via Claude Max account.
• Sessions started as claude --bg --dangerously-skip-permissions --model claude-fable-5-1 "..." from a git worktree; subagents via the Agent tool with the model inherited or passed as claude-fable-5-1.
• Usage credits: on at the time of the spend; off when claude.ai Fable was also refused.

Related
#92576 (Fable blocked behind usage credits despite the plan allowance), #96035 and #97997 (Opus usage counted against the Fable bucket). This report is the inverse: the Fable bucket is unusable once the general bucket is empty, and Fable spend goes to credits instead.