fix: harden linear token sequence matcher

[jbachorik]

Summary

• make cached LinearTokenSequenceMatcher execution state per-call and make bracket-tail scanning linear
• admit the named-capture LTS route only when every Grok-observable named group has a capture-producing plan operation
• add concurrency, projection, and JDK-differential coverage for the expanded Grok access-log fixtures

Why

Grok consumes named capture indexes only. The named-only projection preserves those indexes, but the LTS plan could previously select a route that did not populate every named group. This change declines that route and lets the normal strict compiler choose the implementation instead.

Validation

• ./gradlew --rerun-tasks :reggie-codegen:test --tests '*LinearTokenSequencePlanTest' :reggie-runtime:test --tests '*LinearTokenSequenceMatcherTest' --tests '*LinearTokenSequenceAccessLogTest'
• ./gradlew jacocoVerify build

[codecov-commenter]

Codecov Report

❌ Patch coverage is 94.87179% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 84.4%. Comparing base (f437ac8) to head (5d31eba).

Files with missing lines	Patch %	Lines
...ghq/reggie/runtime/LinearTokenSequenceMatcher.java	95.0%	0 Missing and 3 partials ⚠️
...ggie/codegen/analysis/LinearTokenSequencePlan.java	93.7%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@ Coverage Diff @@## main #111 +/- ##
=======================================
Coverage 84.3% 84.4% Complexity 1 1 =======================================
Files 147 147 Lines 42922 42960 +38 Branches 5845 5851 +6 =======================================
+ Hits 36213 36260 +47 + Misses 4919 4916 -3 + Partials 1790 1784 -6 

Files with missing lines	Coverage Δ
.../com/datadoghq/reggie/runtime/RuntimeCompiler.java	88.3% <100.0%> (+<0.1%)	⬆️
...ggie/codegen/analysis/LinearTokenSequencePlan.java	81.7% <93.7%> (+1.9%)	⬆️
...ghq/reggie/runtime/LinearTokenSequenceMatcher.java	76.9% <95.0%> (+4.7%)	⬆️

... and 1 file with indirect coverage changes

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[Copilot]

Pull request overview

This PR hardens the runtime Linear Token Sequence (LTS) matcher to be safer under concurrency and more correct for Grok-style “named-only” capture projection, while adding targeted regression/performance tests around these behaviors.

Changes:

• Make LTS execution state per-invocation (removing shared scratch arrays) and make bracket-tail scanning linear-time.
• Gate runtime LTS routing on whether the plan actually covers all named capture indexes (avoid selecting an LTS route that can’t populate Grok-observable named groups).
• Add new correctness, JDK-differential, and concurrency tests for named-only routing and bracket scanning edge cases.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
reggie-runtime/src/main/java/com/datadoghq/reggie/runtime/RuntimeCompiler.java	Refines LTS routing by requiring plans to cover all named capture indexes before selecting the LTS matcher.
reggie-runtime/src/main/java/com/datadoghq/reggie/runtime/LinearTokenSequenceMatcher.java	Removes shared scratch state, introduces per-call workspace, and replaces bracket scanning with a linear pass.
reggie-codegen/src/main/java/com/datadoghq/reggie/codegen/analysis/LinearTokenSequencePlan.java	Adds coversCaptureIndexes(...) to verify a plan has capture-producing ops for required group indexes (including inside optional sequences).
reggie-codegen/src/test/java/com/datadoghq/reggie/codegen/analysis/LinearTokenSequencePlanTest.java	Adds unit tests validating capture-coverage semantics (optional nesting, named-group coverage, invalid indexes).
reggie-runtime/src/test/java/com/datadoghq/reggie/runtime/LinearTokenSequenceMatcherTest.java	Adds routing regression test for named-only coverage plus new bracket-scanning edge/perf tests.
reggie-runtime/src/test/java/com/datadoghq/reggie/runtime/LinearTokenSequenceMatcherConcurrencyTest.java	Introduces concurrent-use stress tests for cached LTS matchers and nested optional rollback behavior.

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