feat(opencode): let tools opt into strict mode

[mayshwartz2]

Issue for this PR

Closes #40214

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

Lets a tool ask for strict mode, instead of it being decided only by which provider you're on.

strict?: boolean is added to the tool definition and to the tool.definition plugin hook, and passed to the AI SDK Tool only when explicitly set. The strict: false injection from #33392 for @ai-sdk/openai, @ai-sdk/azure and @ai-sdk/amazon-bedrock/mantle is untouched and still wins, so nothing changes unless a tool opts in.

It reaches the model because strict?: boolean is a documented field on the AI SDK Tool type, @ai-sdk/amazon-bedrock@4.0.112 forwards it into toolSpec, and Bedrock's Converse API enforces it.

Five lines of production code, the rest is tests. AI SDK path only — the TODO at packages/llm/src/protocols/openai-responses.ts:264 is a separate change.

How did you verify your code works?

• Root bun run typecheck: 30/30 tasks pass.
• bun test test/tool/ test/provider/: 872 pass. bun test test/session/ test/plugin/: 536 pass.
• New tests: a custom .opencode/tool declaring strict: true reaches the registry with it set and doesn't leak onto other tools, and it survives LLMRequestPrep.prepare on @ai-sdk/amazon-bedrock while still being forced to false on mantle.
• Checked against Bedrock directly (us.anthropic.claude-sonnet-4-6) that the flag does something: optional properties are fine, additionalProperties must be explicitly false, and minimum/maximum/maxItems are rejected.

Screenshots / recordings

Not a UI change.

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

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