fix(cloudflare-ai-gateway): translate dotted Anthropic ids for the Unified route

[superhighfives]

Summary

Unified billing (and BYOK) is broken for every proxied Anthropic model behind cloudflare-ai-gateway. The Cloudflare AI Gateway's Unified API forwards the requested model id straight through to the upstream provider. models.dev publishes Anthropic ids with dot-separated version numbers to match its site-wide display convention (anthropic/claude-haiku-4.5), but Anthropic's real API model slugs use dashes (claude-haiku-4-5). The unmodified dotted id 404s against Anthropic before the request ever gets a chance to use the gateway's stored/unified-billing credentials.

This is scoped to Anthropic — every other proxied provider in the cloudflare-ai-gateway catalog (OpenAI, xAI, Google, Alibaba, DeepSeek, Moonshot AI, Thinking Machines) already uses dots as part of its actual upstream slug (e.g. OpenAI's gpt-4.1 is really gpt-4.1), so translating dots to dashes only for anthropic/ ids is safe and doesn't touch anyone else.

Root cause / verification

• Reproduced directly against ai-gateway-provider's createUnified() (the same call this plugin makes), bypassing opencode's CLI entirely:
  • anthropic/claude-haiku-4.5 → APICallError: model: claude-haiku-4.5 (not_found_error, straight from Anthropic via the gateway)
  • anthropic/claude-haiku-4-5 → succeeds, billed through the gateway's unified billing with no Anthropic key configured anywhere
• Confirmed this is unrelated to any pending models.dev catalog change: models.dev's cloudflare-ai-gateway provider files for Anthropic models have used the dotted filename/id (with base_model pointing at the dashed lab model, e.g. base_model = "anthropic/claude-haiku-4-5") since before the currently open anomalyco/models.dev#4922, and that PR doesn't touch id/filename conventions. base_model is parse-time-only in models.dev and doesn't propagate into the generated catalog JSON opencode consumes, so the plugin can't recover the native slug from data — it has to derive it.
• A raw curl to the gateway's native /anthropic/v1/messages route (not the Unified API) with no upstream Anthropic key succeeds today, confirming unified billing itself is correctly configured account-side; the bug is purely in how the model id reaches the Unified route.

Change

• packages/core/src/plugin/provider/cloudflare-ai-gateway.ts: add nativeModelId(), which replaces . with - for ids prefixed anthropic/ before calling unified(modelID). No-op for every other provider.
• Added two tests: dotted Anthropic id → dashed id sent to createUnified, and a non-Anthropic dotted id (OpenAI's gpt-4.1) passed through unchanged.

Test plan

• bun test in packages/core — 1095 pass / 0 fail (includes the 2 new cases)
• tsgo --noEmit — clean
• oxlint — 0 new errors (pre-existing warnings only, unrelated to this file)
• Live repro against a real Cloudflare AI Gateway (unified billing enabled, no Anthropic key) confirms the fix

Marked as a draft since I don't have a way to run this through opencode's own CLI test harness end-to-end from this environment — happy to iterate on review.

🤖 Generated with Claude Code

[github-actions]

This PR doesn't fully meet our contributing guidelines and PR template.

What needs to be fixed:

• PR description is missing required template sections. Please use the PR template.

Please edit this PR description to address the above within 2 hours, or it will be automatically closed.

If you believe this was flagged incorrectly, please let a maintainer know.

[github-actions]

Thanks for your contribution!

This PR doesn't have a linked issue. All PRs must reference an existing issue.

Please:

1. Open an issue describing the bug/feature (if one doesn't exist)
2. Add Fixes #<number> or Closes #<number> to this PR description

See CONTRIBUTING.md for details.

[github-actions]

This pull request has been automatically closed because it was not updated to meet our contributing guidelines within the 2-hour window.

Feel free to open a new pull request that follows our guidelines.

[superhighfives]

Reopened as #44251, which meets the contributing guidelines: a short hyphenated branch name (gateway-anthropic-ids, no fix/ prefix), a concise description filling out the PR template, and the single-use helper inlined per the style guide. Same fix.