internal/trace: fix recorder.Write return value for header-only buffers

[jjpinto]

Fix issue #77083

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Message from Gopher Robot:

Patch Set 1:

(1 comment)

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Message from Jorge Pinto:

Patch Set 1:

(1 comment)

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Message from Michael Pratt:

Patch Set 1: Code-Review+1

(1 comment)

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Message from Michael Pratt:

Patch Set 1: Commit-Queue+1

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Message from Go LUCI:

Patch Set 1:

Dry run: CV is trying the patch.

Bot data: {"action":"start","triggered_at":"2026-01-07T01:50:55Z","revision":"35f6875114786a3c769973368e91d6276846f326"}

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Message from Michael Pratt:

Patch Set 1: -Commit-Queue

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Patch Set 1:

This CL has passed the run

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Patch Set 1: LUCI-TryBot-Result+1

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Message from Michael Knyszek:

Patch Set 1: Code-Review+2

(1 comment)

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Message from Michael Knyszek:

Patch Set 1:

(1 comment)

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Message from Michael Knyszek:

Patch Set 1: Commit-Queue+2

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Message from Go LUCI:

Patch Set 1:

CV is trying the patch.

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This PR is being closed because golang.org/cl/734300 has been merged.