[miniflare] Fix Buffer type not accepted for D1 blob bindings

[ascorbic]

Fixes #5771.

The ArrayBufferView devalue reducer serialises typed arrays by constructor name. Node.js Buffer extends Uint8Array, so ArrayBuffer.isView() matches it and serialises ["Buffer", ...]. On the workerd side, the reviver fails because:

1. globalThis.Buffer may not exist in workerd
2. Buffer isn't in ALLOWED_ARRAY_BUFFER_VIEW_CONSTRUCTORS

The fix normalises subclass constructor names to the nearest standard typed array parent in the reducer (not the reviver). This matches structured clone behaviour — Buffer is serialised as Uint8Array, which is what it extends.

This affects anyone passing a Buffer as a D1 bind parameter via getPlatformProxy() or the Miniflare API.

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• Tests
  • Tests included/updated
  • Automated tests not possible - manual testing has been completed as follows:
  • Additional testing not necessary because:
• Public documentation
  • Cloudflare docs PR(s):
  • Documentation not necessary because: Bug fix with no API change

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[claude]

Claude finished @ascorbic's task —— View job

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Changeset Review

✅ All changesets look good

The changeset .changeset/fix-buffer-devalue.md has been validated:

• ✅ Version Type: patch - Correct for a bug fix
• ✅ Changelog Quality: Well-written description with clear explanation of the problem and solution
• ✅ Markdown Headers: No h1/h2/h3 headers present
• ✅ Format: Follows the conventional commit style ("fix: ...") which is acceptable per guidelines
• ✅ Scope: Correctly targets only the miniflare package

The changeset clearly explains:

• What the bug was (Buffer serialization failure)
• Why it happened (Buffer isn't in allowed constructor list)
• How it was fixed (normalize to standard typed array parent)
• Technical context (matches structured clone behavior)

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[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

View in Devin Review to see 2 additional findings.

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commit: fab4e2d

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Latest commit: fab4e2d

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