fix(a2a-server,core-tool): harden host fallback and guard schema definition conflicts

[RuleViz]

This PR fixes two reliability issues across A2A server setup and tool schema generation.

1. In A2A deployment properties, host resolution now falls back to localhost when local IP lookup throws a SocketException, and logs a warning instead of leaving host as null.
2. In tool parameter schema generation, $defs hoisting now detects conflicting definitions for the same key and throws an explicit exception instead of silently overriding previous entries.

The change includes regression tests for both cases:

• deployment host fallback on local IP resolution failure
• $defs merge behavior for both conflicting and equivalent definitions

[CLAassistant]

All committers have signed the CLA.

[Copilot]

Pull request overview

Improves reliability in A2A server deployment defaults and tool JSON Schema generation by adding safer fallbacks and fail-fast behavior for schema definition conflicts.

Changes:

• Fall back to localhost when local IP resolution throws SocketException, and warn with the exception.
• Detect and reject conflicting $defs/definitions entries during schema hoisting instead of silently overwriting.
• Add regression tests covering both the host fallback behavior and $defs conflict/equivalence handling.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
agentscope-extensions/agentscope-extensions-a2a/agentscope-extensions-a2a-server/src/main/java/io/agentscope/core/a2a/server/transport/DeploymentProperties.java	Adds localhost fallback + warning log when local IP lookup fails.
agentscope-extensions/agentscope-extensions-a2a/agentscope-extensions-a2a-server/src/test/java/io/agentscope/core/a2a/server/transport/DeploymentPropertiesTest.java	Updates expectation to assert localhost on local IP lookup failure.
agentscope-core/src/main/java/io/agentscope/core/tool/ToolSchemaGenerator.java	Guards $defs hoisting against conflicting definitions using equality checks + fail-fast exception.
agentscope-core/src/test/java/io/agentscope/core/tool/ToolSchemaGeneratorTest.java	Adds unit tests for conflicting vs equivalent $defs merges via reflective invocation.

[Copilot]

Log message grammar: "fallback" is a noun; as a verb it should be "fall back" (e.g., "...; falling back to default host"). Adjusting this improves readability/searchability in logs.

Suggested change

	"Failed to resolve local IP address, fallback to default host: {}",
	"Failed to resolve local IP address, falling back to default host: {}",

[Copilot]

The IllegalStateException message will be useful for debugging schema generation failures, but it could be more actionable by including whether the conflict came from "$defs" vs "definitions" and a short hint that this can be caused by simple-name collisions under PLAIN_DEFINITION_KEYS. Consider enriching the message accordingly.

Suggested change

	"Conflicting schema definition found for key: " + defKey);
	"Conflicting schema definition found for key '"
	+ defKey
	+ "' while hoisting from '"
	+ key
	+ "'. This can be caused by simple-name collisions when using plain definition keys.");

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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