feat: send custom HTTP headers on Anthropic provider requests

[Ueslei Lima (uesleilima)]

What and why

Anthropic-compatible enterprise gateways often require extra HTTP headers (tenant ID, APIM subscription key, anthropic-version) beyond the API key. This PR adds OPENWIKI_PROVIDER_DEFAULT_HEADERS, a JSON object of header names to string values, and sends them on every Anthropic request via clientOptions.defaultHeaders.

When a custom Anthropic baseURL is set, the client also enables streaming and streamUsage so gateway transports that reject non-streaming requests still work.

Header values can contain secrets, so the env var is persisted as a managed key but treated as a secret: diagnostics redact it, and debug dumps report length only (no preview).

How tested

• Unit tests for resolveProviderDefaultHeaders (empty/invalid JSON, non-string values, invalid header names, successful parse).
• createModel tests for default headers and streaming-when-custom-base-URL (and that neither is forced against api.anthropic.com).
• Redaction tests that header JSON never leaks into diagnostic text or debug previews.
• Env persistence / diagnostics tests that the key is managed and masked.
• Locally: pnpm run format, pnpm run lint, pnpm test (174 files passed, 2340 tests passed).

Changeset

Minor changeset in .changeset/anthropic-default-headers.md — user-facing feature.

Historical context

This was previously bundled with an Anthropic-on-Azure-Foundry provider in #55. This PR isolates custom Anthropic headers (and the related custom-base-URL streaming tweak) as a single concern per CONTRIBUTING.md. It does not add a Foundry provider or HTTP proxy support.

[changeset-bot]

🦋 Changeset detected

Latest commit: 9c389a1

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
openwiki	Minor

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