java: plumb AbortSignal through ToolInvocation for cooperative cancellation

[gimenete]

Summary

Fixes #1433 for the Java SDK.

Adds AbortSignal to ToolInvocation so tool handlers can observe when session.abort() is called and stop in-flight work cooperatively — without needing OS-level process kills. Also adds cancelToolCall(toolCallId) for single-handler cancellation, mirroring the Node.js reference (PR #1701).

Changes

New: AbortSignal class (com.github.copilot.rpc)

public final class AbortSignal {
    public boolean isAborted()               // poll the cancelled state
    public void onAborted(Runnable listener) // register a cancel callback
    public void abort()                      // SDK-internal: fires the signal
}

abort() is idempotent — the signal fires exactly once. Callbacks registered after the signal has already fired are invoked immediately.

Updated: ToolInvocation.getAbortSignal()

ToolHandler handler = invocation -> {
    AbortSignal signal = invocation.getAbortSignal();
    return CompletableFuture.supplyAsync(() -> {
        while (!signal.isAborted()) {
            // do incremental work here
        }
        throw new CancellationException("Tool aborted");
    });
};

Or register a callback:

signal.onAborted(() -> myHttpClient.cancel());

Updated: CopilotSession.abort()

When session.abort() is called, the SDK now:

1. Fires all AbortSignal instances for currently in-flight tool invocations
2. Then sends the existing session.abort RPC as before

New: CopilotSession.cancelToolCall(String toolCallId)

Fires the AbortSignal for only the named in-flight handler — without aborting the agentic loop or other running handlers.

boolean wasCancelled = session.cancelToolCall(toolCallId);
// true  → handler found and signal fired
// false → no in-flight handler with that ID (already completed or unknown)

The activeToolSignals tracking map is keyed by toolCallId (falls back to requestId when toolCallId is null) so cancelToolCall can do a direct map lookup.

New: Java README "Tool Handler Cancellation" section

Documents both cancellation paths with handler examples.

Tests

• ToolInvocationTest: 6 new unit tests for AbortSignal behaviours (idempotent abort, immediate callback when already aborted, null listener rejection, etc.)
• CancelToolCallTest: 3 new unit tests — targeted cancel fires only signal A while signal B stays unaffected; returns false for unknown id; cancelled signal is removed from the map

Confirmed not in PR

• java/mvnw — only modified locally (chmod), not committed

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

This PR introduces cooperative cancellation for tool executions by adding an AbortSignal that propagates from CopilotSession.abort() into each ToolInvocation.

Changes:

• Added AbortSignal type with isAborted(), listener registration, and idempotent abort().
• Wired per-tool AbortSignal creation/management into CopilotSession and exposed it via ToolInvocation#getAbortSignal().
• Added unit tests and package documentation for the new cancellation signal.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 8 comments.

Show a summary per file

File	Description
java/src/main/java/com/github/copilot/rpc/AbortSignal.java	New cancellation signal implementation with listener support.
java/src/main/java/com/github/copilot/rpc/ToolInvocation.java	Adds AbortSignal to tool invocation API + docs.
java/src/main/java/com/github/copilot/CopilotSession.java	Tracks active tool signals and aborts them on session abort.
java/src/main/java/com/github/copilot/rpc/package-info.java	Documents AbortSignal in RPC package overview.
java/src/test/java/com/github/copilot/ToolInvocationTest.java	Adds tests covering AbortSignal and default signal behavior.