fix(agent-core-v2): skip deterministic provider validation retries

[kermanx]

Related Issue

Follow-up to #1598 and its review finding about deterministic provider validation errors.

Problem

The v2 retry fallback introduced in #1598 treats every base ChatProviderError as transient. The Anthropic adapter uses that base error for malformed image data URLs and unsupported base64 image media types before making an HTTP request, so retrying repeats the same deterministic failure, delays the final error, and emits misleading retry events.

What changed

• Exclude the same two client-side image validation message families that v1 already excludes from its base provider-error retry fallback.
• Keep generic unclassified provider failures retryable, along with the existing transient HTTP status handling.
• Add regression coverage for both deterministic validation messages while retaining coverage for the generic fallback.

Validation

• pnpm --filter @moonshot-ai/agent-core-v2 exec vitest run test/app/llmProtocol/errors.test.ts test/agent/stepRetry/stepRetry.test.ts --maxWorkers=2 (105 tests passed)
• pnpm --filter @moonshot-ai/agent-core-v2 test -- --reporter=dot (3,159 tests passed)
• pnpm --filter @moonshot-ai/agent-core-v2 typecheck
• pnpm --filter @moonshot-ai/agent-core-v2 lint:domain
• pnpm exec oxlint --type-aware packages/agent-core-v2/src/app/llmProtocol/errors.ts packages/agent-core-v2/test/app/llmProtocol/errors.test.ts
• pnpm exec changeset status
• pnpm --filter @moonshot-ai/agent-core-v2 dep-graph:lint still reports the 21 pre-existing unresolved IAgentWireService binding errors from main; none of its findings are in files changed by this PR.

Checklist

• I have read the CONTRIBUTING document.
• I have linked a related issue, or explained the problem above.
• I have added tests that prove my feature works.
• Ran gen-changesets skill, or this PR needs no changeset.
• Ran gen-docs skill, or this PR needs no doc update. (No documentation update is needed for this retry-classification bug fix.)

[changeset-bot]

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[pkg-pr-new]

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commit: 3eaa673