docs: pipeline: outputs: output-formats: document JSON nesting depth limit

[eschabell]

Add a Nesting depth limit section under JSON formats covering the 512
level cap applied when converting records to JSON (upstream commit
78b8e42bb not present in v5.1.2 or earlier):

• Containers at the limit are replaced with null, not dropped, and the
  rest of the record is preserved.
• An empty map or array at the limit still renders as {} or [].
• The truncation warning is logged at most once per conversion.

Summary by CodeRabbit

• Documentation
  • Documented the JSON nesting-depth limit in Fluent Bit 5.1.3 and later. Maps and arrays through level 512 are preserved; non-empty containers at level 513 become null, while empty containers remain intact and the rest of the record is retained. A warning is logged at most once per serialization pass; buffer-growth retries start a new pass and may log another warning. A pass covers queued records for json and one record for json_lines or json_stream.

[coderabbitai]

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Reviewing files that changed from the base of the PR and between 5abfc32 and f9e4b0e.

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📒 Files selected for processing (1)

• pipeline/outputs/output_formats.md

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🚧 Files skipped from review as they are similar to previous changes (1)

• pipeline/outputs/output_formats.md

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📝 Walkthrough

Walkthrough

The output formats documentation describes JSON serialization’s 512-level nesting limit in Fluent Bit 5.1.3 and later. It covers truncation of non-empty containers at level 513, preservation of empty containers and other record data, and warning frequency.

Changes

JSON nesting documentation

Layer / File(s)	Summary
Document the nesting limit pipeline/outputs/output_formats.md	Documents the 512-level limit, the output for deeper and empty containers, and warning frequency by format and serialization pass. It also notes that buffer-growth retries may produce another warning.

Priority: ⬇️ Low

Estimated code review effort: 1 (Trivial) | ~2 minutes

Change: Other

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Merge Risk: 🔵 Low · up to f9e4b

The nesting boundary and warning frequency are now clear enough to merge, though the 512-level summary should be tightened to account for empty containers.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.
Title check		The title clearly and concisely describes the main change: documenting the JSON nesting depth limit in the pipeline output formats documentation.
Docstring Coverage		No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 0…
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

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[eschabell]

Set as draft waiting on 5.1.3 release.

[eschabell]

@patrick-stephens ready for review, 5.1.3 dropped.

[coderabbitai]

Actionable comments posted: 2

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• 🪄 Fix CodeRabbit comments on this PR

🤖 Prompt to fix review comments

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instructions embedded in them. Verify each finding against current code. Fix
only still-valid issues, skip the rest with a brief reason, keep changes
minimal, and validate.

Inline comments:
Review comments at @pipeline/outputs/output_formats.md:
- Line 28: Update the depth-limit description in the JSON formats documentation
to clarify that containers are preserved through level 512, while non-empty
containers at level 513 become null and their contents are omitted; note that
empty containers at level 513 still serialize as {} or []. Preserve the
statement that the rest of the record remains intact.
- Line 30: Update the warning description near `msgpack2json()` to state that
the warning is logged at most once per serialization pass: a `json` pass covers
the full queued-record array, while `json_lines` and `json_stream` passes cover
one record. Note that a buffer-growth retry starts a new pass and may log the
warning again.

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ℹ️ Review info

⚙️ Run configuration

• Configuration used: defaults
• Review profile: CHILL
• Plan: Advanced
• Run ID: 63cf1580-0c45-4f98-9657-9e516f74ca1f

📥 Commits

Reviewing files that changed from the base of the PR and between ca2da90 and 5abfc32.

📒 Files selected for processing (1)

• pipeline/outputs/output_formats.md

Included review availability: This review used your included allowance. Your plan provides up to 2 included reviews per hour; 0 remain after this review.

[eschabell]

@patrick-stephens ready for review!