Fix response-tracking and analytics for enforce routes and deployment edges (OSP-101)

[BenItBuhner]

Summary

Fixes OSP-101: response-tracking and analytics were unreliable for some models and routing edges (notably custom deployments like Minimax M3).

Root causes addressed:

1. Enforce mode dropped x-opencode-* headers — OpenAI routes built session headers but EnforceRouter never forwarded them to FallbackRouter, breaking upstream/session-scoped response counting when enforce was enabled.
2. Winning route never recorded — recordRequestFinish supported resolvedProvider / resolvedModel but routes only logged the logical model, so per-edge analytics in the dashboard showed –.
3. No lifetime counters — the dashboard only reflected the last fetched window (15 records), not responses since process start.
4. Reasoning models misclassified as empty — enforce treated content: null + reasoning_content as empty, causing false retries/failures for models like Minimax M3.
5. Deployment URL templates ignored — {model} / {{model}} in provider endpoint paths (e.g. Azure-style deployments) were not substituted.
6. Streaming client aborts orphaned logs — aborted streams could skip recordRequestFinish.

Changes

• Thread extraHeaders and resolvedRoute through EnforceRouter → FallbackRouter
• Record winning provider/model on every finish path (OpenAI + Anthropic)
• Add process-lifetime request_stats to /health/detailed and /v1/admin/logs
• Dashboard Responses card now shows finished count since start with ok/err breakdown
• Treat reasoning_content / reasoning / thinking as non-empty in enforce validation
• Substitute {model} in buildEndpointUrl using upstream model id
• Shared buildUpstreamExtraHeaders helper; Anthropic routes now forward session headers too
• Stream cancel() handler logs client-aborted requests (status 499)

Testing

• bun test tests/enforce-router.test.ts tests/enforce-validator.test.ts tests/request-log.test.ts tests/provider-helpers.test.ts tests/fallback-router.test.ts — all pass
• Full suite: 148 pass (3 pre-existing opencode-provider config fixture failures unrelated to this change)
• bun run typecheck — passes (excluding pre-existing models-list.test.ts typing noise)

Linear

Resolves OSP-101

Linear Issue: OSP-101