fix(combo): stop premature context compaction — real auto-combo windows + per-target compression limit

[diegosouzapw]

Problem

Reported in a (since-deleted) discussion: auto combos mis-detect max context, producing too-small context windows and premature auto-compaction — the coding agent "keeps forgetting things".

Tracing the full chain surfaced two real bugs plus the mechanism that ties them together:

Bug 1 — auto combos advertise limit.context = 0 (client side)

GET /api/combos/auto never exposed any context info, so the opencode plugin hardcoded limit: { context: 0, output: 0 } for auto combos (mapAutoComboToStaticEntry).

opencode's overflow guard short-circuits on zero (packages/opencode/src/session/overflow.ts):

if (input.model.limit.context === 0) return false  // never overflow

→ smart auto-compaction is silently disabled for auto combos. The session grows unbounded until OmniRoute's server-side purifyHistory() (compression Layer 3) starts destructively dropping old messages on every turn — the agent forgets context with no client-visible signal.

Bug 2 — chatCore compresses DB combos at min(...allTargets) (server side)

chatCore.ts proactive compression overrode the context limit with the minimum across every combo target, even though chatCore always executes per concrete target (handleSingleModel resolves provider/model before delegating). A combo with a 1M-window primary and a 32k sibling compressed every request at 32000 × 0.7 — including requests served by the 1M target. Quota-shared pools (DB combos under the hood) hit the same path.

Fix

Layer	Change
virtualFactory.ts	New computeAdvertisedLimits() — MAX of candidates' context windows / max output tokens, exposed as advertisedContextLength / advertisedMaxOutputTokens
GET /api/combos/auto	Serves context_length + max_output_tokens per variant
opencode plugin	mapAutoComboToStaticEntry consumes the served limits; safe positive fallback (128000 / 8192) for older servers — never 0
contextManager.ts	New resolveComboContextLimit() — uses the executing target's own window; min(...targets) kept only as defensive fallback when the current provider/model resolves no specific limit
chatCore.ts	Combo compression block wired to the helper

Why MAX for auto combos: the auto-combo context pre-filter (combo.ts — estimated-tokens filter + filterTargetsByRequestCompatibility, which runs for all strategies) already routes oversized requests to large-window candidates, so advertising the largest window is safe and lets client compaction calibrate to the best candidate. Decision approved by maintainer; /v1/models LCD (MIN) policy for DB combos is deliberately unchanged.

Investigation answers (asked in the report)

• How do we manage differing context sizes across combo targets? Catalog: MIN-of-targets (LCD, unchanged). Routing: per-request compatibility filter skips too-small targets (all strategies). Compression: was min-of-all (bug) → now per-executing-target.
• Codex context-relay combo: orthogonal mechanism — watches codex quota (85%/95% thresholds, contextHandoff.ts), generates a structured LLM summary and injects it on account switch. It preserves context across accounts, not window sizing. Untouched.
• Quota-shared: quotaShared-* are DB combos (fill-first) created without context_length; they inherit catalog MIN and hit the chatCore combo path — Bug 2's fix covers them.

Validation (Rule #18 — TDD)

• RED→GREEN: tests/unit/auto-combo-context-advertising.test.ts (8 tests: MAX aggregation, route advertising, per-target limit + regression cases) and @omniroute/opencode-plugin/tests/auto-combo-context.test.ts (3 tests: served limits, old-server fallback, non-positive rejection)
• Plugin suite: 257/257 · vitest (autoCombo): 146/146 · affected unit files: 57/57
• typecheck:core clean · lint clean · check:cycles clean · docs-sync + any-budget gates green
• Full test:unit: 19 failures, all verified pre-existing/flaky — same names fail on clean base a3253399b (13), plus the known chatcore-translation-paths cycle drift ([BUG] Valid max_tokens-truncated response misclassified as "empty content" → fake 502 #3572) and 4 suite-parallelism flakes that pass isolated (4/4)

[gemini-code-assist]

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[diegosouzapw]

Merged into release/v3.8.22 ✅ — fixes the premature context-compaction chain (auto-combo now advertises real context_length/max_output_tokens instead of 0, and chatCore compresses against the executing target's window, not min(...allTargets)). 8 server + 3 plugin TDD tests green. Ships in the next release.

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

This PR fixes a critical two-part bug in auto-combo context-window handling:

1. Client-side fix: /api/combos/auto now advertises context_length/max_output_tokens (MAX of candidate pool) instead of hardcoding 0, which was causing opencode to disable its smart auto-compaction entirely.
2. Server-side fix: chatCore compression now uses the executing target's own window via resolveComboContextLimit(), with min(...targets) kept only as a defensive fallback.

The implementation is sound:

• resolveComboContextLimit() correctly prioritizes target-specific limits
• computeAdvertisedLimits() uses MAX safely (pre-filter routes oversized requests to large-window candidates)
• Both functions have comprehensive TypeScript safety and positive fallbacks (128000/8192)
• 11 TDD tests cover the expected behavior

The PR is already merged and all tests/quality gates pass.

Files Reviewed (6 files)

• open-sse/services/contextManager.ts - New resolveComboContextLimit() function
• open-sse/services/autoCombo/virtualFactory.ts - New computeAdvertisedLimits() function
• open-sse/handlers/chatCore.ts - Wired to use per-target compression limit
• src/app/api/combos/auto/route.ts - Exposes context_length/max_output_tokens
• @omniroute/opencode-plugin/src/index.ts - Consumes served limits with fallback
• tests/unit/auto-combo-context-advertising.test.ts - TDD tests
• @omniroute/opencode-plugin/tests/auto-combo-context.test.ts - Plugin TDD tests

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_{Reviewed by laguna-m.1-20260312:free · 2,044,614 tokens}