docs: processors: cumulative-to-delta: add new processor documentation

[eschabell]

  - Add pipeline/processors/cumulative-to-delta.md for the new
    processor_cumulative_to_delta plugin
  - Document all five config options: initial_value, drop_first,
    drop_on_reset, max_staleness, max_series
  - Explain what gets converted (monotonic sums, histograms, exp
    histograms) and what passes through (non-monotonic sums, gauges)
  - Document reset detection, out-of-order sample dropping, and
    staleness/memory eviction behavior
  - Add configuration examples for auto, keep, and drop_first modes
  - Add SUMMARY.md entry alphabetically within the Processors section

  Fixes #2478

Summary by CodeRabbit

• Documentation
  • Added documentation for the Cumulative to Delta processor, including configuration options, metric conversion behavior, reset detection handling, sample management, state eviction controls, and usage examples.

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⚙️ Run configuration

Configuration used: defaults

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Run ID: b3cc5171-8567-496c-92e6-62462b19f8b8

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Reviewing files that changed from the base of the PR and between 6b22239 and 352d80f.

📒 Files selected for processing (1)

• pipeline/processors/cumulative-to-delta.md

📝 Walkthrough

Walkthrough

This PR adds documentation for a new "cumulative to delta" metrics processor that converts cumulative monotonic metric types into delta-style values. The addition includes updating the table of contents and providing a comprehensive reference document with configuration parameters and examples.

Changes

Cohort / File(s)	Summary
Documentation & Navigation SUMMARY.md, pipeline/processors/cumulative-to-delta.md	Added new processor documentation file describing cumulative-to-delta conversion functionality, including configuration parameters (initial_value, drop_first, drop_on_reset, max_staleness, max_series), reset detection behavior, and two YAML configuration examples. Updated SUMMARY.md to link the new documentation entry under Processors.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

Possibly related issues

• Doc updates needed from 1 Mar - 18 Mar (based on code updates) #2477: Directly addresses the same documentation addition for the cumulative-to-delta processor page and SUMMARY.md entry.
• New processor needed for Cumulative to Delta #2478: Directly addresses the same cumulative-to-delta processor documentation file and corresponding navigation update.

Suggested reviewers

• cosmo0920
• patrick-stephens

Poem

🐰 Metrics that climb now dance and leap,
From cumulative heights to deltas deep,
With config in hand and examples so clear,
The processor's story now shines bright here! ✨

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and specifically describes the main change: adding documentation for a new processor (cumulative-to-delta) with appropriate scope prefix (docs: processors:).
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Inline comments:
In `@pipeline/processors/cumulative-to-delta.md`:
- Around line 91-107: The YAML examples for the cumulative_to_delta processor
are partial fragments and may be mistaken for full configs; update the
documentation around the two snippets to say they are fragment overrides to be
placed inside an input's processors.metrics block (or expand each into a minimal
surrounding context showing an input -> processors -> metrics -> - name:
cumulative_to_delta block), and mention the relevant keys (cumulative_to_delta,
processors.metrics, initial_value, drop_first) so readers know where to insert
them.

---

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Configuration used: defaults

Review profile: CHILL

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Run ID: f7d5dd05-9c22-4ab2-ac0f-7038d6392bb3

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Reviewing files that changed from the base of the PR and between 21b6f3c and 6b22239.

📒 Files selected for processing (2)

• SUMMARY.md
• pipeline/processors/cumulative-to-delta.md

[eschabell]

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[eschabell]

@patrick-stephens and @lecaros and @cosmo0920 This is a new plugin we are adding for processing, could use a review to make sure I did not miss anything?