feat: add native full capture spans

[jbachorik]

Adds a conservative direct native full-capture LTS profile for the logs migration stack.\n\n- preserves numeric spans for admitted source captures\n- fails closed on unproven capture/control-flow transforms\n- keeps legacy named-only routing and caches isolated\n\nValidation: spotlessApply; focused runtime tests; :reggie-runtime:test.

[Copilot]

Pull request overview

This PR extends the native linear-token-sequence (LTS) admission path to a conservative full-capture profile, exposing numeric capture spans (groupCount(), start(int), end(int)) while remaining native-only (no JDK fallback) and keeping the legacy/general compiler caches isolated.

Changes:

• Add a direct “full-capture LTS” compilation path in RuntimeCompiler, with stricter admission checks around capture layout and deterministic boundaries.
• Expose numeric capture-group span APIs on ReggieMatchState and expand runtime tests to validate JDK-equivalent numeric spans (including unmatched optional captures) and cache isolation.
• Add AST-level validation (CaptureProjection.fullCaptureLayout) and update documentation describing the July 2026 adoption progress and remaining work.

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
reggie-runtime/src/test/java/com/datadoghq/reggie/runtime/ReggieCompiledPatternTest.java	Adds/updates tests for numeric spans, rejection shapes, DOTALL behavior, cache isolation, and input mutation safety.
reggie-runtime/src/test/java/com/datadoghq/reggie/runtime/InterruptibleCharSequenceTest.java	Adjusts interruption regression coverage to avoid now-rejected alternation shapes under full-capture admission.
reggie-runtime/src/main/java/com/datadoghq/reggie/runtime/RuntimeCompiler.java	Implements full-capture LTS admission and supporting deterministic-boundary/capture-layout validation.
reggie-runtime/src/main/java/com/datadoghq/reggie/runtime/ReggieNativeCapability.java	Updates capability documentation to refer to full-capture LTS.
reggie-runtime/src/main/java/com/datadoghq/reggie/runtime/ReggieMatchState.java	Adds groupCount(), start(int), and end(int) for numeric source capture spans.
reggie-runtime/src/main/java/com/datadoghq/reggie/runtime/ReggieCompileFlag.java	Updates documentation to reflect the full-capture LTS flag profile.
reggie-runtime/src/main/java/com/datadoghq/reggie/runtime/ReggieCompiledPattern.java	Routes native compilation through the new full-capture LTS admission.
reggie-runtime/src/main/java/com/datadoghq/reggie/runtime/ReggieCompilationResult.java	Updates documentation to reflect full-capture native compilation.
reggie-runtime/src/main/java/com/datadoghq/reggie/runtime/ReggieCompilationRejection.java	Adds MISSING_CAPTURE to represent missing numeric capture preservation requirements.
reggie-codegen/src/main/java/com/datadoghq/reggie/codegen/analysis/CaptureProjection.java	Adds fullCaptureLayout to validate a conservative numeric capture layout at the AST level.
doc/plans/logs-backend.md	Updates migration/adoption planning documentation and clarifies current capabilities/limitations.

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Codecov Report

❌ Patch coverage is 63.97849% with 67 lines in your changes missing coverage. Please review.
✅ Project coverage is 84.4%. Comparing base (61206a8) to head (ba547cb).

Files with missing lines	Patch %	Lines
.../com/datadoghq/reggie/runtime/RuntimeCompiler.java	58.0%	14 Missing and 38 partials ⚠️
...ghq/reggie/codegen/analysis/CaptureProjection.java	68.7%	2 Missing and 13 partials ⚠️

❌ Your patch status has failed because the patch coverage (63.9%) is below the target coverage (70.0%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@ Coverage Diff @@## agent/logs-reggie-l1k #121 +/- ##
=========================================================
- Coverage 84.5% 84.4% -0.1% 
Complexity 1 1 =========================================================
Files 156 156 Lines 43277 43460 +183 Branches 5910 5985 +75 =========================================================
+ Hits 36571 36702 +131 - Misses 4913 4917 +4 - Partials 1793 1841 +48 

Files with missing lines	Coverage Δ
...om/datadoghq/reggie/codegen/automaton/CharSet.java	90.2% <ø> (ø)
...ghq/reggie/runtime/LinearTokenSequenceMatcher.java	81.9% <100.0%> (+0.6%)	⬆️
...ghq/reggie/runtime/ReggieCompilationRejection.java	100.0% <100.0%> (ø)
...adoghq/reggie/runtime/ReggieCompilationResult.java	73.3% <ø> (ø)
...om/datadoghq/reggie/runtime/ReggieCompileFlag.java	100.0% <ø> (ø)
...atadoghq/reggie/runtime/ReggieCompiledPattern.java	100.0% <100.0%> (ø)
...com/datadoghq/reggie/runtime/ReggieMatchState.java	100.0% <100.0%> (ø)
...tadoghq/reggie/runtime/ReggieNativeCapability.java	100.0% <ø> (ø)
...ghq/reggie/codegen/analysis/CaptureProjection.java	63.6% <68.7%> (+3.3%)	⬆️
.../com/datadoghq/reggie/runtime/RuntimeCompiler.java	84.4% <58.0%> (-3.7%)	⬇️

... and 2 files with indirect coverage changes

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