refactor(combo): move handleRoundRobinCombo into roundRobinCombo.ts

[HouMinXi]

Summary

Move handleRoundRobinCombo (and resolveTargetTokenLimit) from open-sse/services/combo.ts into open-sse/services/combo/roundRobinCombo.ts.

This branch is stacked on #12746 (feat/combo-execute-target-split @ 5a5ee9be5), which is still open. GitHub will list Inner's 7 commits plus the 3 below. After #12746 lands, rebase this onto release/v3.8.51 and the Inner SHAs drop.

This PR's own commits (on top of #12746):

1. 4d168211d — source guards (RED on ENOENT before the lift)
2. 13219a86b — the lift
3. changelog fragment

If you want a PR that contains only those three, wait for #12746 to merge and I will rebase. Opening now because the lift is done and reviewed against combo.ts:189/202/759.

What this PR owns (vs #12746)

	After #12746	This PR
combo.ts	2164	1014 (split("\n").length)
roundRobinCombo.ts	—	1199 (cap 1200)
handleRoundRobinCombo	still in combo.ts	leaf module

Files vs #12746 (not vs tip):

• open-sse/services/combo.ts (−1178 net)
• open-sse/services/combo/roundRobinCombo.ts (new)
• tests/unit/combo/round-robin-combo.test.ts (new)
• tests/unit/combo/combo-attempt-loop.test.ts (rrStart === -1 so Inner's unused-delay assert cannot false-green after the name leaves combo.ts)
• changelog.d/maintenance/combo-round-robin-extract.md

Cycle

The leaf still static-imports releaseStickyPinOnFailure and clearStaleLKGP from ../combo.ts (combo.ts:189 / :202). Those helpers stay on the barrel because Inner / executeTargetAttempt take them via deps.

The barrel does not static-import the leaf. The round-robin fork is:

const { handleRoundRobinCombo } = await import("./combo/roundRobinCombo.ts");

at combo.ts:759. Node caches the module after the first load.

What did not change

Round-robin skip / sticky / semaphore / rrLoopSafetyTimer finally are copied as-is. This does not run Inner's 10 executeTarget gates on RR (breaker OPEN still does not skip an RR rotate; it only clears sticky). A later PR can add a shared targetPolicy if we want that table filled per view.

Tests

DISABLE_SQLITE_AUTO_BACKUP=true node --max-old-space-size=8192 \
  --import tsx/esm --import ./open-sse/utils/setupPolyfill.ts \
  --import ./tests/_setup/isolateDataDir.ts --test --test-force-exit \
  tests/unit/combo/round-robin-combo.test.ts \
  tests/unit/combo/combo-attempt-loop.test.ts \
  tests/unit/combo-loop-safety-timer-leak-11804.test.ts

12/12 pass. Injection: deleting releaseStickyPinOnFailure( in the leaf turns the guard red; restore is green.

node scripts/check/check-file-size.mjs --base-ref upstream/release/v3.8.51 OK. npx eslint --no-cache on the four unique files: 0 errors.

Not in this PR

• Feeding Inner gates into RR (would change rotation)
• targetPolicy.ts
• chatCore.ts
• fix(combo): treat a pin-only step as implicit connection allowlist #12697 pin allowlist, fix(dashboard): batch delete no longer toasts failure after success #12711 batch-delete, fix(dashboard): moonshot voucher/cash leftover follows bucket balance #12733 moonshot bar, fix(glm): drop extra 16th arg to SSE transform helper #12770 glm arity, fix(claude): extra-usage switch does not skip 5h preflight #12803 extra-usage, feat(grok-cli): show and redeem banked reset credits on Provider Limits #12805 grok resets

Base-red inherited

⚠️ base-red inherited: #12732 (release/v3.8.51 currently red). Failures that match that issue are not from this lift. Unique diff does not touch glm.ts, reset-aware-model-family.md, or agent-skills cli-tunnel.

[HouMinXi]

Rebased onto release/v3.8.51 tip f9a1cc8a9 (#12682 / #12691 / #12834).

3135e5ca0 → efee49419. range-diff 10 commits =. GPG G. No file overlap with the three landed commits.

[HouMinXi]

Rebased onto upstream/release/v3.8.51 b345c7f6c (#12870 OpenCode v2 plugin).

• efee49419ae → ddd6bcbfcc5
• range-diff identity (eq=3 unique); all commits GPG G
• 10 unique commit(s) ahead, 0 behind
• --force-with-lease to HouMinXi:feat/combo-round-robin-extract
  Stacked onto rebased Inner refactor(combo): split executeTarget into gates, attempt, and loop #12746 (152bf96db). Seven Inner commits skipped as already applied; three unique RR commits range-diff =.