Fix openRouter streamed citation end offsets overwrite start offsets - #7128

Reviewed changes

• packages/ai/openrouter/test/OpenRouterLanguageModel.test.ts: added a streamText regression test that asserts streamed URL citations preserve both startIndex and endIndex under metadata.openrouter.
• Confirmed the test reproduces the described bug: the current source emits { openrouter: { startIndex: 9 } } instead of { openrouter: { startIndex: 2, endIndex: 9 } }.

⚠️ Implementation fix is missing

The regression test is correct and well-targeted, but this branch does not yet contain the actual fix. The streaming citation path in packages/ai/openrouter/src/OpenRouterLanguageModel.ts still has the typo at line 1364:

...(Predicate.isNotUndefined(annotation.url_citation.end_index)
  ? { startIndex: annotation.url_citation.end_index }  // should be endIndex
  : undefined)

The non-streaming path at lines 1099–1104 already uses endIndex correctly, so the fix is a one-line key rename in the streaming branch.

Suggested next steps

1. Apply the one-line fix in OpenRouterLanguageModel.ts (change the duplicated startIndex key to endIndex in the streaming citation block).
2. Re-run pnpm test --run packages/ai/openrouter/test/OpenRouterLanguageModel.test.ts -t "preserves streamed citation start and end indexes" to confirm the test passes.
3. Add a changeset for the runtime fix before merging.

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✅ No new issues found.

Reviewed changes

This incremental review covers the commits pushed since the prior Pullfrog review. The previously missing implementation fix is now present, along with a changeset.

• Fixed the streaming citation key typo in packages/ai/openrouter/src/OpenRouterLanguageModel.ts: the end_index value is now assigned to endIndex instead of overwriting startIndex, matching the non-streaming path.
• Added a changeset for @effect/ai-openrouter describing the streamed citation offset fix.
• Reformatted the HttpClientResponse.fromWeb call in the new makeStreamTestLayer helper for readability.

Validation run: pnpm --filter @effect/ai-openrouter test --run test/OpenRouterLanguageModel.test.ts, pnpm lint-fix, and pnpm check all passed.

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