Issue for this PR

Closes #30648

Type of change

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

What does this PR do?

Fixes a hook consistency gap for file parts in prompt resolution.

Previously, when resolving non-text/non-directory file parts (e.g. image/binary attachments), SessionPrompt.resolvePart read the file directly and created a data URL without invoking plugin read hooks. As a result, tool.execute.before did not fire for image/binary file reads.

This PR updates that branch to trigger Read-equivalent hooks:

• tool.execute.before with args: { filePath }
• file read execution
• tool.execute.after with a minimal output payload (Binary read successfully)

Behavior is otherwise preserved: attachments are still forwarded as data URLs.

Also included:

• preserve error observability parity in this branch (log.error + Session.Event.Error)
• regression test in packages/opencode/test/session/prompt.test.ts verifying both tool.execute.before and tool.execute.after fire for image file parts and receive expected arguments.

How did you verify your code works?

• Added regression test:
  • fires tool.execute.before for image file parts
• Attempted to run targeted test from packages/opencode:
  • bun test test/session/prompt.test.ts -t "fires tool.execute.before for image file parts"
• In this environment test execution is blocked by pre-existing workspace/module resolution errors:
  • Cannot find module '@opencode-ai/llm' from packages/core/src/session/event.ts

Screenshots / recordings

Not included.

Checklist

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