test(coding-agent): correct custom discovery limit contract

[Yeachan-Heo]

Summary

• correct the issue fix(providers): restore YAML model override precedence over discovered contextWindow after #3927 #3954 regression fixture: the old deepseek-r1 expectation had no same-id models entry or modelOverrides entry
• prove explicit same-id YAML fields beat a distinct discovery context_length
• cover exact-id discovered-only modelOverrides field precedence and uncatalogued UNK_* fallback

No runtime provider-discovery source changed; model configuration remains identity-scoped with no cross-id inheritance.

Verification

• bun test packages/coding-agent/test/issue-970-custom-provider-discovery.test.ts — 3 pass, 0 fail
• bun test packages/coding-agent/test/model-registry.test.ts --test-name-pattern "discoverable bundled replacement survives refresh" — 1 pass, 0 fail
• bun test packages/coding-agent/test/model-registry.test.ts --test-name-pattern "modelOverrides still apply after discoverable refresh" — 1 pass, 0 fail
• bun test packages/coding-agent/test/model-registry.test.ts --test-name-pattern "newly discovered ids inherit provider fields, not another model's custom fields" — 1 pass, 0 fail
• bun x biome check packages/coding-agent/test/issue-970-custom-provider-discovery.test.ts
• git diff --check

Closes #3954

—
[repo owner's gaebal-gajae (clawdbot) 🦞]

[Yeachan-Heo]

Red-team review — MERGE_READY / CLEAR

Exact head: 460285d137066278bc63d5ab275b519957bab3e1
Base: dev @ d2646cb8a (mergeable: true)

Scope (exact-head diff)

Surface	Result
Files	1 only — packages/coding-agent/test/issue-970-custom-provider-discovery.test.ts
Production / runtime code	None
Commits	1 — test(coding-agent): correct custom discovery limit contract

Contract correction (not a behavior change)

The prior assertion treated sibling-discovered models as inheriting YAML fields from a different model id (deepseek-r1 expected contextWindow: 128000 / maxTokens: 8192 from qwen3.6). That is not the post-#3927 discovery contract.

Corrected contract under test:

1. Same-id YAML wins over discovery payload (qwen3.6 keeps YAML 128000/8192 even when discovery reports context_length: 256000).
2. modelOverrides apply per discovered id (issue-3954-override-context → 64000; issue-3954-override-max → maxTokens 4096 while keeping discovered context_length).
3. Uncatalogued discovery-only models use UNK_CONTEXT_WINDOW / UNK_MAX_TOKENS placeholders — not hardcoded sibling inheritance.

Runtime paths (model-registry.ts, discovery, providers) are untouched. This is a test-oracle fix only.

CI evidence (exact head)

Check class	Result
Affected path validation + evidence producer	success
Targeted test issue-970-custom-provider-discovery.test.ts	success
ts-build coding-agent	success
native-build, gjc-state-gates, Telegram generation guard	success
Local public surfaces	failure — pre-checkout only: Failed to resolve action download info → Internal Server Error / Service Unavailable (GitHub Actions 5xx). No repository code executed. Documented infrastructure flake; not a product regression.
Windows / Python / darwin / Live release	correctly skipped

Regression risk

Risk	Verdict
Silent runtime change	No — zero production files
Weakens discovery guarantees	No — tightens oracle to real precedence (YAML same-id, modelOverrides, UNK fallbacks)
Masks #3927 breakage	No — CI targeted suite green at this head against post-#3927 code

Verdict

MERGE_READY / CLEAR. Owner-authored T0 unblock. Safe to merge to dev despite Local public surfaces infrastructure 5xx.

— census red-team @ emergency audit batch