fix(gateway): keep reasoning on unpinned routing

[steebchen]

Problem

Reasoning was silently dropped for Claude models on AWS Bedrock when the model was requested without a provider prefix.

Requested model	Routed to	Reasoning before
aws-bedrock/claude-opus-4-6 (pinned)	aws-bedrock	✅ yes
claude-opus-4-6 (unpinned)	aws-bedrock	❌ none (reasoning_tokens: 0)

Reported by users via RisuAI: reasoning_effort: high on claude-opus-4-6 / claude-opus-4-8 produced no <Thoughts> / delta.reasoning / reasoning tokens, but the same request pinned to aws-bedrock/... worked.

Root cause

useExpandedRoutingProviders is true only when a provider is explicitly requested. For unpinned routing, modelInfo.providers keeps only the region-agnostic root mapping (region: undefined) — region expansion (expandProviderRegions) is never applied to it. Meanwhile routing still resolves usedRegion to a concrete value (AWS Bedrock's global, pinDefaultRegion: true).

The capability lookup in chat.ts matched on exact region equality:

modelInfo.providers.find(p => p.providerId === usedProvider && p.region === usedRegion)

'global' !== undefined → no match → supportsReasoning = false (and splitTaggedReasoning / healStreamingJsonOutput) → prepareRequestBody skipped the entire thinking block → Bedrock Claude returned no reasoning.

Fix

Resolve the mapping with a region-agnostic fallback — prefer the exact (providerId, region) mapping, otherwise fall back to the provider-level mapping. Capability flags (reasoning, reasoningMode, splitTaggedReasoning, healStreamingJsonOutput) cannot be overridden per region (ProviderRegion only permits pricing/context/output/streaming overrides), so the base mapping carries identical flags to every regional variant and the fallback is lossless. Extracted into a pure selectProviderMapping helper in @llmgateway/actions with unit tests.

Verification

Live against AWS Bedrock (gateway run locally with real Bedrock key):

Case	Before	After
unpinned claude-opus-4-6 → bedrock	0 reasoning tokens	187
unpinned claude-opus-4-8 → bedrock	0 reasoning tokens	160
pinned aws-bedrock/claude-opus-4-6:global	reasons	reasons (no regression)
anthropic/claude-opus-4-6	reasons	reasons (no regression)
unpinned claude-haiku-4-5 (no reasoning support)	400	400 (not over-enabled)

• New unit test fails before the fix and passes after.
• pnpm format and full pnpm build pass; existing prepare-request-body reasoning specs unchanged.
• Adversarially reviewed for sibling bugs: the other (providerId, region) lookups in the rate-limit/uptime fallback and dev-plan paths are gated by requestedProvider (the pinned path, where providers are already region-expanded), so they are not affected.

🤖 Generated with Claude Code

Summary by CodeRabbit

• Bug Fixes

  • Improved provider capability detection (including reasoning support) by resolving the correct provider/region mapping with reliable region-agnostic fallbacks when an exact region entry isn’t present.

• Tests

  • Added a new test suite covering provider mapping resolution scenarios: exact region matches, region-agnostic fallback selection, order independence, no-match behavior, and handling of undefined regions.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

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Run ID: 750b3053-4194-4432-9acb-cc139d9719ef

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Reviewing files that changed from the base of the PR and between bb836b5 and bcba97e.

📒 Files selected for processing (1)

• apps/gateway/src/chat/tools/resolve-provider-context.ts

---

Walkthrough

A new selectProviderMapping function is added to packages/actions that resolves a ProviderModelMapping by first attempting an exact (providerId, region) match and falling back to a region-agnostic match. It is exported from the package index and used in the gateway chat and provider context resolution modules to replace direct providers.find(...) calls, ensuring capability flags like supportsReasoning remain accurate when provider mappings are not region-expanded.

Changes

selectProviderMapping helper and gateway integration

Layer / File(s)	Summary
selectProviderMapping helper implementation and tests packages/actions/src/select-provider-mapping.ts, packages/actions/src/select-provider-mapping.spec.ts	Implements selectProviderMapping with exact (providerId, region) lookup and region-agnostic fallback, documented with a comment explaining the resolution order and why the fallback is needed. Five Vitest cases cover: root-only fallback, exact region preference, order-independent behavior, no-match undefined return, and region-less mapping selection.
Package export and gateway integration packages/actions/src/index.ts, apps/gateway/src/chat/chat.ts, apps/gateway/src/chat/tools/resolve-provider-context.ts	Re-exports selectProviderMapping from the actions package index; the gateway chat and provider context resolution modules import and call it in place of direct modelInfo.providers.find(...) lookups for provider mapping resolution and supportsReasoning detection.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~12 minutes

Possibly related PRs

• theopenco/llmgateway#2033: Both PRs modify apps/gateway/src/chat/chat.ts to ensure usedRegion is accurate—main PR relies on usedRegion to resolve provider mappings via selectProviderMapping, while the retrieved PR fixes usedRegion being stale in the low-uptime fallback path.
• theopenco/llmgateway#2224: Both PRs adjust how the selected provider model mapping is resolved with fallback logic to prevent capability flags like supportsReasoning from being dropped when provider/region mapping mismatches occur.

Suggested reviewers

• smakosh

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'fix(gateway): keep reasoning on unpinned routing' directly and concisely summarizes the main change: fixing a bug where reasoning capability was dropped during unpinned routing to AWS Bedrock.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@packages/actions/src/select-provider-mapping.ts`:
- Around line 26-28: The fallback logic in the provider find chain does not
explicitly target the region-agnostic root mapping as described in the function
contract. The current second find returns any first match with the providerId,
but it should specifically look for a provider with region set to undefined
before falling back to any generic provider lookup. Modify the fallback chain to
add an explicit intermediate check that searches for a provider with the
matching providerId and region explicitly set to undefined, ensuring the
fallback behavior follows the documented contract and is not order-dependent on
provider array ordering.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: 54856e33-ac23-4774-9191-74c58bdf6742

📥 Commits

Reviewing files that changed from the base of the PR and between dc7aba7 and f78b06c.

📒 Files selected for processing (4)

• apps/gateway/src/chat/chat.ts
• packages/actions/src/index.ts
• packages/actions/src/select-provider-mapping.spec.ts
• packages/actions/src/select-provider-mapping.ts

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Reuse region fallback for retry context

This fixes the initial request, but retry/fallback requests still rebuild the provider context through resolveProviderContext, which exact-matches modelInfo.providers on (providerId, region) at apps/gateway/src/chat/tools/resolve-provider-context.ts:378 and derives supportsReasoning from that result at line 415. For unpinned AWS Bedrock routing, modelInfo.providers can still contain only the root mapping while usedRegion is global, so any retry after a transient upstream/key failure will send the retried request without reasoning even though the first attempt now includes it. Use the same fallback helper in the retry context path as well.

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