fix: size the 1M context window for the bracket alias form (opus[1m]) - #302
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`contextWindowForModel` matched only the `-1m` suffix, so the bracket form
Claude Code actually emits — `opus[1m]`, `claude-opus-5[1m]` — fell through to
the conservative 200k default. Asking EXPLICITLY for the 1M variant therefore
sized the window WORSE than the bare `opus` alias, which resolves to 1M.
Observed on a live session pinned to `opus[1m]`: codeoid computed a 200k window
against ~999k of real usage. Affected consumers:
- the percent-of-window figure on SessionInfo (session.ts) — reads ~500%
- the fork / provider-switch seed budget (seedBudgetChars via
targetContextWindow) — 5x too small, so history seeds over-truncate
Auto-rotate is NOT affected: decideRotation is passed the static
`Session.CONTEXT_WINDOW` (1M), not this per-model resolution.
This also did NOT cause the "prompt is too long" overflow seen on that session
— that has a separate cause (compaction firing reactively after the API error
rather than proactively). This is an independent defect surfaced while
investigating it.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
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The bug
contextWindowForModelmatched only the-1msuffix, so the bracket form Claude Code actually emits —opus[1m],claude-opus-5[1m]— fell through to the conservative 200k default.The result inverts caller intent: asking explicitly for the 1M variant sized the window worse than the bare alias.
opus[1m]sonnet[1m]claude-opus-5[1m]opushaikuHow it surfaced
Found while investigating a real
prompt is too long: 1000076 tokens > 1000000 maximumon a live session pinned toopus[1m], where codeoid computed a 200k window against ~999k of actual usage.Blast radius (traced, not assumed)
Affected — the two production consumers of this function:
SessionInfo(session.ts:2826) — reads ~500% occupancyseedBudgetCharsviatargetContextWindow) — 5× too small, so history seeds over-truncateNot affected:
decideRotationis passed the staticSession.CONTEXT_WINDOW(hardcoded1_000_000), not this per-model resolution. An earlier revision of this description claimed otherwise; that was wrong.What this does not fix
It did not cause that overflow. The rotation path never consulted this value, and separately, under-sizing would make rotation fire earlier rather than later. The overflow has an independent cause — compaction firing reactively after the API error rather than proactively at a threshold — which is upstream SDK behavior and is being tracked separately.
Verification
lint+typecheckclean, 2370 pass / 0 fail. Four regression assertions on the bracket form including case-insensitivity, plus ahaikuguard so a bracket suffix can't manufacture a 1M window where no such variant exists.🤖 Generated with Claude Code