fix(cli): attribute step events to their model in run json output

[Enough1122]

Issue for this PR

Closes#40544

Type of change

• Bug fix

What does this PR do?

opencode run --format json emitted step_start/step_finish without any model reference, so a headless consumer could not attribute tokens or cost - especially across mid-session model switches or subagents running a different model. The core session.step.started event already carries the model (the human output prints it), so the JSON path now stamps providerID/modelID onto step_start from the event and onto step_finish from the in-flight capture, clearing it when the step ends.

How did you verify your code works?

• bun run typecheck (packages/cli): clean
• additive keys on JSON events; the v1-compatibility pendingStep path inherits them through the same part object

Screenshots / recordings

Not a UI change.

Checklist

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

[github-actions]

Thanks for your contribution!

This PR doesn't have a linked issue. All PRs must reference an existing issue.

Please:

1. Open an issue describing the bug/feature (if one doesn't exist)
2. Add Fixes #<number> or Closes #<number> to this PR description

See CONTRIBUTING.md for details.

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Potential Duplicate Found

PR #40545: fix(opencode): add model attribution to run --format json events
#40545

This PR appears to be directly related to the current PR #44462. Both are focused on adding model attribution (providerID/modelID) to run --format json output. PR #40545 specifically addresses model attribution to events, which is exactly what the current PR is doing for step events.

Since the current PR (#44462) closes issue #40544 and is also about attributing step events to their model in JSON output, you should verify whether #40545 already addresses this or if they're complementary changes to different aspects of the same feature.

[Enough1122]

Heads up that #40545 (fix(opencode): add model attribution to run --format json events) opened earlier covers the same issue. Not attached to landing this separately - happy to consolidate or close in favor of it if the maintainers prefer that approach; leaving this up because it ships with its own tests that could be salvaged either way.

[Enough1122]

Similar work landed in #40545 against packages/opencode/src/cli/cmd/run.ts, which no longer exists on v2 (the noninteractive runner lives in packages/cli/src/run/noninteractive.ts now). This PR carries the same attribution over to the current tree.