[kaahos]

What does this PR do?:
Encode debug unwind-failure event sizes with a multi-byte JFR varint.

Motivation:
Long runtime-stub names can exceed the one-byte event-size limit. Reserve a complete size prefix so debug recordings retain valid event boundaries instead of aborting or becoming unreadable.

Additional Notes:

• Stacked on fix(profiler): mark skipped frozen virtual-thread callers as truncated #877. The complete delta is three encoding/test files; carrier recovery remains in feat(profiler): recover carrier ancestry at continuation boundaries #887 and native unwinding in fix(profiler): recover arm64 native stacks across sampling signals #917.
• The event schema and release recording behavior are unchanged. Diagnostics require DEBUG.
• Independent full-diff source review: passed, with no actionable findings.

How to test the change?:

./.claude/commands/build-and-summarize :ddprof-lib:gtestDebug \
  :ddprof-lib:gtestRelease_unwindFailureEncoding_ut qualityChecks

Validation for 966e098, including the reviewed documentation-only prerequisite update:

Check	State	Result
macOS ARM64 full native debug	passed	Full suite on refreshed prerequisite
Encoding regressions	passed	Six name lengths, diagnostic fields, maximum counters and following-event boundary
Release encoding guard	passed	Explicit skip because debug diagnostics are compiled out
macOS ARM64 affected Java smoke	passed	Six active cases; seven existing mode skips
Formatting and quality checks	passed	spotlessApply, qualityChecks, diff check
Full PR scope	passed	Encoding delta byte-identical after prerequisite update
Remote CI	passed	113 reported checks succeeded; no failures or pending checks

For Datadog employees:

• If this PR touches code that signs or publishes builds or packages, or handles credentials of any kind, I've requested a security review.
• This PR doesn't touch any of that.
• JIRA: PROF-16298

[dd-octo-sts]

CI Test Results

Run: #41051492859 | Commit: 9efc022 | Duration: 19m 18s (longest job)

✅ All 108 test jobs passed

Status Overview

JDK	glibc-aarch64/asan	glibc-aarch64/debug	glibc-aarch64/release	glibc-aarch64/tsan	glibc-amd64/asan	glibc-amd64/debug	glibc-amd64/release	glibc-amd64/tsan	musl-aarch64/debug	musl-aarch64/release	musl-amd64/debug	musl-amd64/release
8	-	-	-	-	✅	✅	✅	✅	-	-	-	-
8-ibm	-	-	-	-	✅	✅	✅	✅	-	-	-	-
8-j9	✅	✅	✅	✅	✅	✅	✅	✅	-	-	-	-
8-librca	-	-	-	-	-	-	-	-	✅	✅	✅	✅
8-orcl	-	-	-	-	✅	✅	✅	✅	-	-	-	-
11	-	-	-	-	✅	✅	✅	✅	-	-	-	-
11-j9	✅	✅	✅	✅	✅	✅	✅	✅	-	-	-	-
11-librca	-	-	-	-	-	-	-	-	✅	✅	✅	✅
17	✅	✅	✅	✅	✅	✅	✅	✅	-	-	-	-
17-graal	✅	✅	✅	✅	✅	✅	✅	✅	-	-	-	-
17-j9	✅	✅	✅	✅	✅	✅	✅	✅	-	-	-	-
17-librca	-	-	-	-	-	-	-	-	✅	✅	✅	✅
21	✅	✅	✅	✅	✅	✅	✅	✅	-	-	-	-
21-graal	✅	✅	✅	✅	✅	✅	✅	✅	-	-	-	-
21-librca	-	-	-	-	-	-	-	-	✅	✅	✅	✅
25	✅	✅	✅	✅	✅	✅	✅	✅	-	-	-	-
25-graal	✅	✅	✅	✅	✅	✅	✅	✅	-	-	-	-
25-librca	-	-	-	-	-	-	-	-	✅	✅	✅	✅

Legend: ✅ passed | ❌ failed | ⚪ skipped | 🚫 cancelled

Summary: Total: 108 | Passed: 108 | Failed: 0

---

Updated: 2026-10-30 13:36:55 UTC

[dd-octo-sts]

✅ All 40 integration tests passed

📊 Dashboard · 👷 Pipeline · 📦 d1b347f6

[kaahos]

@codex review

[chatgpt-codex-connector]

Codex Review Summary

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-28T13:24:43.908939Z	966e098	Manual request

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[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. More of your lovely PRs please.

Reviewed commit: 9ee9826193

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[kaahos]

@codex review

[datadog-datadog-us1-prod]

More details

The reserved five-byte prefix matches the existing JFR varint writer, preserving event boundaries for long debug unwind-failure names without changing release behavior.

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Reviewed commit: 966e0983e9

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[datadog-datadog-us1-prod]

More details

The reserved varint prefix accommodates bounded unwind-failure names while preserving event boundaries and diagnostic fields. Source review also found the continuation-truncation changes consistent with their callers and regression tests.

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