Apply provider context window settings to occupancy lookups

[TheGreatAxios]

Summary

• Applies providers.<name>.contextWindow at config load so occupancy, compaction, and the status-bar meter honor the setting
• Keys the override as <provider>:<model> for every model on a provider that sets the field, plus the bare model id for the resolved provider
• Leaves the known OAuth-projection gap: Codex/xAI synthetic settings still drop the field

Verification

• bun run typecheck, bun run build, and bun run test pass
• bun run check passes (6957 pass, 0 fail)

Fixes CL-7762

[linear-code]

CL-7762

[TheGreatAxios]

Critic · Comment

Wires providers.<name>.contextWindow into contextWindowFor at loadConfig after resolveProvider. Overrides beat registry/heuristic; OAuth projection still drops the field.

Findings

• src/provider/context-window.ts:111 — override lookup reuses registry lookupCandidates, so a prefixed id for a provider that did not set contextWindow still hits the resolved provider's bare key. Sequence: firepass {models:["fp-large"], contextWindow:32000} + other {models:["fp-large"]} (no window), resolve firepass; contextWindowFor("other:fp-large") and hasContextWindowFor("other:fp-large") return 32k / true via candidate fp-large. Occupancy uses bare source.model / config.model, so the meter still honors the startup provider; the model-catalog provider:model path does not. Production already writes <provider>:<model> for every overridden provider — exact override match would keep the bare-key rule without this bleed. The unit test at context-window.test.ts:45 encodes the fallthrough by setting only a bare map.

Notes

• OAuth gap is documented, not silently copied (providersAsSettings omits the field; settingsForResolution overwrites). Leave it.
• Bare keys stay frozen at the loadConfig-resolved provider. After /agent switch, compaction (lastModel = event.source?.model) and the status-bar meter (state.config.model) miss the other provider's override; maxTokensFor still reads live settings. Matches the stated keying; not a merge blocker.