[Java] Add PlatformDetector and NativeRuntimeLoader for native binary extraction and caching (tasks 4.2 + 4.3)

[Copilot]

Implements the PlatformDetector utility (task 4.2) and NativeRuntimeLoader (task 4.3) in the new com.github.copilot.ffi package. Tasks 4.1/4.2 were previously merged as empty commits, so this PR delivers both.

PlatformDetector (ffi/PlatformDetector.java)

Pure-Java classifier detection for selecting the correct runtime.node binary:

• OS: os.name → darwin | linux | win32
• Arch: os.arch aliases → x64 | arm64
• Linux libc: reads /proc/self/exe, parses ELF PT_INTERP segment for musl (/ld-musl-) vs. glibc (/ld-linux-)
• detectClassifier() → one of 8 validated classifiers (linux-x64, linuxmusl-arm64, darwin-x64, win32-x64, …); unsupported tuples fail fast

NativeRuntimeLoader (ffi/NativeRuntimeLoader.java)

Resolves runtime.node via:

1. COPILOT_CLI_PATH env var (returned as-is)
2. Classpath resource native/<classifier>/runtime.node → extracted to ~/.copilot/runtime-cache/<version>/<classifier>/runtime.node
3. Sibling of bundled CLI

Extraction is atomic: write to a UUID-named temp file in the same directory, Files.move(ATOMIC_MOVE). If another process wins the race, accepts the winner after a regular/non-empty check. No file locks. No execute bit set (JNA dlopen doesn't require it). Abandoned temp files cleaned in finally.

Version is read from copilot-runtime.properties (Maven resource-filtered ${project.version}). A missing, blank, or unfiltered placeholder is a hard error.

// Resolution usage (task 4.4 will pass this path to JNA)
Path runtimeNode = NativeRuntimeLoader.resolve();

Supporting changes

• copilot-runtime.properties — version=${project.version}, filtered at build time
• pom.xml — Maven <resources> block enables filtering for that one file only
• NativeRuntimeLoaderException — typed checked exception for all failure modes
• Test resource native/linux-x64/runtime.node (stub binary for unit tests)

• Fixes [Java] Embed Rust CLI runtime 4.3: Native binary extraction and caching #2145

[Copilot]

Pull request overview

Adds Java FFI platform detection and native runtime extraction/caching.

Changes:

• Detects OS, architecture, and Linux libc classifiers.
• Resolves and atomically caches runtime.node.
• Adds Maven-filtered version metadata and unit-test fixtures.

Show a summary per file

File	Description
java/pom.xml	Enables version resource filtering.
java/src/main/resources/copilot-runtime.properties	Supplies artifact version metadata.
java/src/main/java/com/github/copilot/ffi/PlatformDetector.java	Implements platform classification.
java/src/main/java/com/github/copilot/ffi/NativeRuntimeLoader.java	Implements runtime resolution and caching.
java/src/main/java/com/github/copilot/ffi/NativeRuntimeLoaderException.java	Defines loader failures.
java/src/test/java/com/github/copilot/ffi/PlatformDetectorTest.java	Tests platform detection.
java/src/test/java/com/github/copilot/ffi/NativeRuntimeLoaderTest.java	Tests loader behavior.
java/src/test/resources/native/linux-x64/runtime.node	Provides a stub native resource.

Review details

Comments suppressed due to low confidence (1)

java/src/main/java/com/github/copilot/ffi/PlatformDetector.java:265

• These two individually valid 32-bit values are added as an int, so a malformed PT_INTERP can overflow end, bypass the bounds check, and cause ArrayIndexOutOfBoundsException. That unchecked exception escapes detectLinuxLibc() instead of producing UNKNOWN; compute and validate the end offset as a long before casting.

            int start = (int) pOffset;
            int end = start + (int) pFileSize;
            if (end > size) {

• Files reviewed: 8/8 changed files
• Comments generated: 7
• Review effort level: Medium

[github-actions]

Cross-SDK Consistency Review ✅

This PR adds PlatformDetector and NativeRuntimeLoader in the com.github.copilot.ffi package — Java-internal infrastructure for locating and extracting the native runtime.node binary at runtime.

No cross-SDK consistency issues found. Here's why:

• Java-specific concern: Embedding and extracting a platform-specific binary from a JAR is a Java packaging constraint. Other SDKs handle CLI resolution differently by design:
  • Node.js: Uses native Node bindings — no extraction needed
  • Python: Invokes the CLI via subprocess using an environment-resolved path
  • Go: Uses os/exec with COPILOT_CLI_PATH or PATH lookup
  • .NET: Uses Process with environment-resolved path
  • Rust: Uses std::process::Command with environment-resolved path
• Internal package: The ffi package is not part of the public SDK API surface (CopilotClient, session management, tool registration), so no parallel public API changes are needed in other SDKs.
• Environment variable parity: The COPILOT_CLI_PATH env var fallback is already the standard cross-SDK mechanism for overriding CLI path — this PR correctly honors it, staying consistent with all other SDKs.

The PR is well-scoped to a Java-specific need and does not introduce any cross-language API inconsistencies.

Generated by SDK Consistency Review Agent for #2157 · sonnet46 17.9 AIC · ⌖ 8.24 AIC · ⊞ 6.6K · ◷

[edburns]

@copilot review

[Copilot]

@copilot review

Reviewed the current state of the PR. All CI workflows pass on commit 406ae3c. Here's a summary:

Addressed in the previous commit (406ae3c):

• COPILOT_RUNTIME_PATH is now a dedicated override distinct from COPILOT_CLI_PATH; the CLI path is only used for the sibling fallback (step 3)
• Tests call production NativeRuntimeLoader.extractToCache(), resolve(), and loadVersion(ClassLoader) directly rather than test-only reimplementations
• Override precedence verified via NativeRuntimeLoader.resolve(runtimeOverride, ...) with assertions that the explicit path is returned before extraction
• Isolated classloader injection used for version-loading failure cases
• PlatformDetectorTest uses parameterized tuple-driven tests with production classifier derivation, including rejection of unsupported OS/arch tuples
• ELF PT_INTERP parsing validates class-specific minimum program-header entry sizes (≥56 bytes for ELF64, ≥32 bytes for ELF32) using long arithmetic to prevent overflow

No new issues found. Formatting passes (spotless:check). The build requires JDK 25+ per the enforcer rule, which is satisfied in CI.