fix(cli): OpenCode config missing limit.output for metadata-less models (#10940)

[diegosouzapw]

Closes #10940

Root cause

src/lib/cli-helper/config-generator/opencode.ts::buildModelEntry() only emitted the limit block when at least one of context / userOutput / catalogOutput resolved to a value. A model with no catalog metadata (no context_length, no max_output_tokens) and no existing user override in opencode.json got no limit block at all — but limit.output is a REQUIRED field in OpenCode's v1 provider schema (configV1), so OpenCode rejected the whole config at startup with Missing key provider.omniroute.models.{model}.limit.output.

Fix

entry.limit is now always emitted, seeded with the already-computed output fallback (catalog value → user override → 8192 default). context and input are added only when actually resolved — we still never fabricate a context window.

Tests

• New regression test tests/unit/opencode-limit-output-10940.test.ts: RED on the untouched code (confirmed — entry.limit was undefined for a metadata-less model), GREEN after the fix.
• Updated the pre-existing #8849 emits a complete limit for catalog metadata without fabricating one test in tests/unit/cli-helper/config-generator.test.ts, which asserted the old (buggy) limit === undefined behavior for a no-metadata model — that assertion was itself encoding the [BUG] Missing key provider.omniroute.models.{model}.limit.output #10940 bug, so it's now aligned to limit: { output: 8192 }.
• Full sibling sweep green: tests/unit/cli-helper/config-generator.test.ts, tests/unit/opencode-config-dir-single-source.test.ts, tests/unit/rotation-config-omniroute.test.ts, tests/unit/cli/configure-command.test.ts (54/54 passing before adding the new file; 36/36 in the two most relevant files after).

Gates run locally

• node scripts/check/check-file-size.mjs — OK (file unchanged in line count)
• node scripts/check/check-complexity.mjs — OK (2615 vs baseline 2774)
• node scripts/check/check-cognitive-complexity.mjs — OK (1175 vs baseline 1223)
• npm run typecheck:core — clean
• npx eslint (suppressions-location config/quality/eslint-suppressions.json) on touched files — 0 errors
• node scripts/check/check-changelog-integrity.mjs — OK

Note (out of scope)

tests/integration/opencode-config-startup.test.ts is separately red on this base tip due to an unrelated pre-existing version-pin drift (OPENCODE_VERSION = "1.18.8" hardcoded vs the installed opencode-ai@1.18.18 from #10931) — confirmed present on origin/release/v3.8.50 before this branch, not touched here.

⚠️ base-red inherited: #9985 — public-creds(copilot-m365-web), docs-sync(PROVIDER_REFERENCE)