ci: report Java to Kotlin migration progress on pull requests

[nickolas-dimitrakas]

Summary

Implements the progress report and the "no new Java" ratchet that the migration playbook describes.

• scripts/kotlin_migration_progress.py measures android-core/src/main and android-kit-base/src/main and reports, per module and in total: Kotlin LOC, Java LOC, Java that stays by design, Java left to convert, Kotlin share, and conversion progress against the 16,550-line baseline measured at 4ee3ba4c. Line counts match wc -l, so the numbers agree with the tracker.
• scripts/kotlin-migration-facades.txt lists the 65 Java files that stay Java (the public API customers and kit authors compile against, per the playbook's Scope section, plus every package-info.java). At main they total 11,287 LOC.
• New job Kotlin Migration Progress runs on every pull request: it measures the head and the base branch (the base with the head's facade list, so editing the list cannot masquerade as progress), posts a sticky comment with the table, and fails when the pull request adds Java to the published modules unless it carries the allow-new-java label. It is not in the required-check set.
• scripts/test_kotlin_migration_progress.py covers the counting, the facade exclusion, the renderers and the clamping; CI runs it first.
• TRACKER.md gains the 0.8 row and a "Checkpoints and expected numbers" table with the Java-left, conversion-progress and estimated Kotlin-share values expected at each stack and checkpoint; PLAYBOOK.md and AGENTS.md mention the job.

Verification

• Unit tests: 5 passing.
• Against main (4ee3ba4c): Java left 16,550, facade 11,287, Kotlin share 12.0%, conversion progress 0.0%.
• The measure step's arithmetic was exercised locally against a main checkout as the base; on this stack it correctly reports the seams added by test: expose explicit test seams for package-private core internals #845 as new Java, which is the expected ratchet signal for that change.

Follow-up

The allow-new-java label does not exist yet and needs creating in the repository settings, alongside api-change-approved from #843.

🤖 Generated with Claude Code

[github-actions]

Kotlin migration progress

No change to the Java left to convert.

Module	Kotlin LOC	Java LOC	Java staying (facade)	Java left to convert	Kotlin share
android-core	3,238	22,515	9,636	12,879	12.6%
android-kit-base	557	5,380	1,651	3,729	9.4%
Total	3,795	27,895	11,287	16,608	12.0%

Conversion progress: 0.0% (16,608 of 16,550 baseline Java LOC left to convert). 132 Java files and 36 Kotlin files in scope.

[github-actions]

📦 SDK Size Impact Report

What the SDK adds to a minified release APK.

Measured against an empty baseline app. Unlike the Rokt kit, android-core ships no Compose and no resources, so there is nothing here that a host app would already provide.

mParticle Core SDK

Metric	Target branch	This PR	Change
APK size	119.79 KB	119.79 KB	-1 bytes
Download size	117.60 KB	117.60 KB	+3 bytes
Dex bytes	213.75 KB	213.75 KB	0 bytes

➡️ SDK size impact change is minimal.

Raw measurements

Target branch:

{"baseline_dex_bytes": 0, "baseline_download_bytes": 2512, "baseline_install_bytes": 7528, "core_dex_bytes": 218884, "core_download_bytes": 122936, "core_install_bytes": 130189}

This PR:

{"baseline_dex_bytes": 0, "baseline_download_bytes": 2511, "baseline_install_bytes": 7528, "core_dex_bytes": 218884, "core_download_bytes": 122938, "core_install_bytes": 130188}

_{Measured 86c46f6 merged into c2e7df5}

[cursor]

PR Summary

Low Risk
The changes only add CI reporting scripts, workflow jobs, and documentation without affecting SDK production runtime code.

Overview
Adds tooling and CI automation to track the Java-to-Kotlin migration progress across android-core and android-kit-base.

Introduces scripts/kotlin_migration_progress.py and unit tests to measure Java and Kotlin lines of code, conversion progress against baseline, and overall Kotlin share. Files defined in scripts/kotlin-migration-facades.txt are counted separately as designated Java facades that remain in Java by design.

Adds the Kotlin Migration Progress GitHub Actions workflow job to .github/workflows/pull-request.yml. The job posts sticky progress comments on pull requests and enforces a ratchet step that fails PRs introducing new Java without the allow-new-java label. Also updates migration documentation and checkpoints in PLAYBOOK.md, TRACKER.md, and AGENTS.md.

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Cursor Bugbot has reviewed your changes using default effort and found 1 potential issue.

There are 2 total unresolved issues (including 1 from previous review).

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[github-actions]

Binary compatibility

• ✅ android-core is compatible with 6.1.5 (115 classes compared, 1 with additions only).
• ✅ android-kit-base is compatible with 6.1.5 (44 classes compared, 0 with additions only).

Compares the release AAR against the same artifact at the last version published to Maven Central; R8-renamed classes and members are excluded (see the script docstring). Full japicmp HTML/XML reports are attached as the api-compat-reports workflow artifact. This check is not in the required-check set yet, so a red result here does not block merging.

[jamesnrokt]

Approved and re-ran checks