fix(hono): resolve "ReadableStream is locked" error in AI SDK

[nadaniels]

🔗 Linked issue

Closes #382

📚 Description

Using createUIMessageStreamResponse or createAgentUIStreamResponse from the Vercel AI SDK inside a Hono route would throw ERR_INVALID_STATE: ReadableStream is locked when running under @hono/node-server.

Root cause: The middleware called createObservedBody(c.res.body) (which calls body.getReader(), locking the stream) and then relied on Hono's compose to update c.res with the wrapped response via the middleware return value. However, Hono skips that update when context.finalized is already true — which is always the case after a route handler returns a Response. This left c.res pointing at the original response whose body was now locked, so @hono/node-server's subsequent response.body.getReader() call threw.

Fix: Explicitly assign c.res = await finishResponse(c.res, ...) instead of returning the wrapped response, so c.res is always updated regardless of context.finalized.

Added additional regression tests

Summary by CodeRabbit

Release Notes

• Bug Fixes

  • Fixed a critical streaming response issue in Hono integration that caused "ReadableStream is locked" errors when using Vercel AI SDK streaming helpers.

• Tests

  • Added comprehensive test coverage for streaming responses in Hono integration, including Server-Sent Events (SSE) behavior and context handling validation.

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: ASSERTIVE

Plan: Pro Plus

Run ID: 167bf827-e4d0-4016-81e1-afe8beb1827d

📥 Commits

Reviewing files that changed from the base of the PR and between 963e7c7 and e2a33c9.

📒 Files selected for processing (3)

• .changeset/salty-apes-find.md
• packages/evlog/src/hono/index.ts
• packages/evlog/test/frameworks/hono.test.ts

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📝 Walkthrough

Walkthrough

This PR fixes the ERR_INVALID_STATE: ReadableStream is locked error that occurs when Hono middleware is used with Vercel AI SDK streaming responses. The fix explicitly reassigns c.res to the finished response in deferred-emission paths, and includes new streaming-focused tests to verify the behavior.

Changes

Streaming ReadableStream Lock Fix

Layer / File(s)	Summary
Deferred-response reassignment for streaming packages/evlog/src/hono/index.ts, .changeset/salty-apes-find.md	The Hono middleware now directly assigns c.res = await finishResponse(c.res, {...}) in deferred-emission paths instead of creating a new Response wrapper, ensuring the finished response and its unlocked body stream state are always set on the context. The changeset documents this as a patch fix for issue #382.
Streaming response test validation packages/evlog/test/frameworks/hono.test.ts	New test suite verifies that streaming text/event-stream responses do not lock the response body before caller reads, and that evlog correctly defers calling drain until the stream closes while capturing mid-stream context updates.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~12 minutes

Possibly related PRs

• HugoRCD/evlog#367: The retrieved PR implements streaming-aware deferred "wide-event" emission across integrations (including Hono) via shouldDeferEmitForResponse/finishResponse plumbing, and the main PR's Hono-specific change reassigns c.res = await finishResponse(...) to make that deferred/finished response handling work correctly for streaming (preventing the locked-body race).

Suggested labels

bug

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely summarizes the main fix: resolving the ReadableStream locked error in Hono with AI SDK integration.
Description check	✅ Passed	The PR description comprehensively covers the linked issue, root cause analysis, the implemented fix, and mentions regression tests; it follows the template structure with linked issue and detailed description sections.
Linked Issues check	✅ Passed	The PR directly addresses all requirements from #382: prevents the middleware from locking the response body and ensures compatibility with Hono/@hono/node-server when streaming AI SDK responses.
Out of Scope Changes check	✅ Passed	All changes are directly scoped to the bug fix: changeset entry, Hono middleware fix, and related regression tests; no unrelated modifications detected.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

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