fix(do): metric-buffer shipped as a binary file (raw NUL bytes)

[prisis]

packages/do/src/metric-buffer.ts is currently a binary blob on alpha — its metric series key used a raw NUL byte (0x00) as the separator, so git classifies the whole ~170-line module as binary. It's invisible in git diff, git blame, and PR review (it shipped that way via #149).

Fix

• Convert the raw NUL separators to the unicode escape sequence — byte-identical at runtime, valid UTF-8 text on disk. The module is now reviewable again.
• Guard against recurrence: scripts/no-nul-bytes.mjs runs in vis.config.ts's staged pre-commit chain (before Prettier, which doesn't catch NUL bytes) and rejects any staged source file containing a raw NUL — with a message pointing at the escape. Tested: rejects a NUL file (exit 1), passes clean files, robust to deleted paths.

Verified: @lunora/do typechecks; the file reads as UTF-8 text with 0 NUL bytes; the fixing commit itself passed the new guard.

(The same fix also rides in #158's rebase, but this isolates it so alpha stops carrying a binary source file independently of that PR's review.)

🤖 Generated with Claude Code

https://claude.ai/code/session_019M6G6CAoLVrQMxDYg7BWq2

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Review skipped

Review was skipped as selected files did not have any reviewable changes.

💤 Files selected but had no reviewable changes (2)

• packages/do/src/metric-buffer.ts
• scripts/no-nul-bytes.mjs

⛔ Files ignored due to path filters (1)

• vis.config.ts is excluded by none and included by none

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📥 Commits

Reviewing files that changed from the base of the PR and between f073c2a and 2bcb413.

⛔ Files ignored due to path filters (1)

• vis.config.ts is excluded by none and included by none

📒 Files selected for processing (2)

• packages/do/src/metric-buffer.ts
• scripts/no-nul-bytes.mjs

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[github-actions]

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[codspeed-hq]

Merging this PR will not alter performance

✅ 160 untouched benchmarks
⏩ 1 skipped benchmark¹

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_{Comparing fix/metric-buffer-nul (2bcb413) with alpha (d1ebb51)²}

Footnotes

1. 1 benchmark was skipped, so the baseline result was used instead. If it was deleted from the codebase, click here and archive it to remove it from the performance reports. ↩

2. No successful run was found on alpha (f073c2a) during the generation of this report, so d1ebb51 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩