perf(upgrade): use copy-then-mmap for zero JS heap during delta patching

[BYK]

Changes

1. Copy-then-mmap with child process probe for mmap safety

Bun.mmap() on the running binary fails fatally on macOS (SIGKILL from AMFI) and
Linux (ETXTBSY). PR #343 fixed this by using arrayBuffer() unconditionally, but that
spikes ~100 MB onto the JS heap.

This PR restores zero-heap mmap while handling the macOS SIGKILL:

1. Copy: copyFileSync(process.execPath, tmpdir/sentry-patch-old-{pid})
   CoW reflinks on btrfs/xfs/APFS for near-instant zero-I/O copy
2. Probe: Spawn a child process that tries Bun.mmap(copy)
   If macOS AMFI sends SIGKILL, only the child dies — parent survives and knows mmap is unsafe
3. Mmap: If probe exits 0, mmap the copy (zero JS heap, kernel-managed pages)
4. Fallback: If probe fails, read copy via arrayBuffer() (~100 MB heap)

2. Instrument delta upgrade with Sentry spans and error capture

Delta failures were completely invisible in Sentry — no spans, no captureException,
errors logged at debug level. The ETXTBSY/SIGKILL bugs (PRs #339–#343) were only
discoverable through code analysis and local reproduction.

• Wraps attemptDeltaUpgrade in withTracingSpan('upgrade.delta')
• Records delta.from_version, delta.to_version, delta.channel, delta.patch_bytes
• On error: captureException with warning level + delta context tags
• Upgrades error log from log.debug() to log.warn() so users see failures

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Semver Impact of This PR

🟢 Patch (bug fixes)

📋 Changelog Preview

This is how your changes will appear in the changelog.
Entries from this PR are highlighted with a left border (blockquote style).

---

New Features ✨

Trace

• Add cursor pagination to trace list by BYK in #324
• Add sentry trace logs subcommand (Add CLI support for fetching logs associated with a trace #247) by BYK in #311

Other

• (api) Add --data/-d flag and auto-detect JSON body in fields by BYK in #320
• (formatters) Render all terminal output as markdown by BYK in #297
• (install) Add Sentry error telemetry to install script by BYK in #334
• (issue-list) Global limit with fair distribution, compound cursor, and richer progress by BYK in #306
• (log-list) Add --trace flag to filter logs by trace ID by BYK in #329
• (logger) Add consola-based structured logging with Sentry integration by BYK in #338
• (project) Add project create command by betegon in #237
• (upgrade) Add binary delta patching via TRDIFF10/bsdiff by BYK in #327
• Improve markdown rendering styles by BYK in #342

Bug Fixes 🐛

Api

• Use numeric project ID to avoid "not actively selected" error by betegon in #312
• Use limit param for issues endpoint page size by BYK in #309
• Auto-correct ':' to '=' in --field values with a warning by BYK in #302

Formatters

• Expand streaming table to fill terminal width by betegon in #314
• Fix HTML entities and escaped underscores in table output by betegon in #313

Setup

• Suppress agent skills and welcome messages on upgrade by BYK in #328
• Suppress shell completion messages on upgrade by BYK in #326

Upgrade

• Replace Bun.mmap with arrayBuffer on all platforms by BYK in #343
• Replace Bun.mmap with arrayBuffer on macOS to prevent SIGKILL by BYK in #340
• Use MAP_PRIVATE mmap to prevent macOS SIGKILL during delta upgrade by BYK in #339

Other

• (ci) Generate JUnit XML to silence codecov-action warnings by BYK in #300
• (install) Fix nightly digest extraction on macOS by BYK in #331
• (nightly) Push to GHCR from artifacts dir so layer titles are bare filenames by BYK in #301
• (project create) Auto-correct dot-separated platform to hyphens by BYK in #336
• (region) Resolve DSN org prefix at resolution layer by BYK in #316
• (test) Handle 0/-0 in getComparator anti-symmetry property test by BYK in #308
• (trace-logs) Timestamp_precise is a number, not a string by BYK in #323

Documentation 📚

• Document SENTRY_URL and self-hosted setup by BYK in #337

Internal Changes 🔧

Api

• Upgrade @sentry/api to 0.21.0, remove raw HTTP pagination workarounds by BYK in #321
• Wire listIssuesPaginated through @sentry/api SDK for type safety by BYK in #310

Other

• (craft) Add sentry-release-registry target by BYK in #325
• (project create) Migrate human output to markdown rendering system by BYK in #341

• (upgrade) Use copy-then-mmap for zero JS heap during delta patching by BYK in #344

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_{🤖 This preview updates automatically when you update the PR.}

[github-actions]

Codecov Results 📊

✅ 101 passed | Total: 101 | Pass Rate: 100% | Execution Time: 0ms

📊 Comparison with Base Branch

Metric	Change
Total Tests	📉 -2582
Passed Tests	📉 -2582
Failed Tests	—
Skipped Tests	—

All tests are passing successfully.

✅ Patch coverage is 88.43%. Project has 3680 uncovered lines.
❌ Project coverage is 80.66%. Comparing base (base) to head (head).

Files with missing lines (1)

File	Patch %	Lines
delta-upgrade.ts	94.39%	⚠️ 24 Missing

Coverage diff

@@            Coverage Diff             @@
##          main       #PR       +/-##
==========================================
- Coverage    82.64%    80.66%    -1.98%
==========================================
  Files          127       127         —
  Lines        17902     19028     +1126
  Branches         0         0         —
==========================================
+ Hits         14794     15348      +554
- Misses        3108      3680      +572
- Partials         0         0         —

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Generated by Codecov Action

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Cursor Bugbot has reviewed your changes and found 1 potential issue.

Autofix Details

Bugbot Autofix prepared a fix for the issue found in the latest run.

• ✅ Fixed: Temp file leaked if writer.end() throws in finally
  • Nested writer.end() in try/finally to ensure cleanupOldFile() always runs even when writer.end() throws.

Or push these changes by commenting:

@cursor push f3adb8e178

Preview (f3adb8e178)

diff --git a/src/lib/bspatch.ts b/src/lib/bspatch.ts
--- a/src/lib/bspatch.ts
+++ b/src/lib/bspatch.ts
@@ -358,8 +358,11 @@
       oldpos += seekBy;
     }
   } finally {
-    await writer.end();
-    cleanupOldFile();
+    try {
+      await writer.end();
+    } finally {
+      cleanupOldFile();
+    }
   }
 
   // Validate output size matches header

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Cursor Bugbot has reviewed your changes and found 2 potential issues.

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