feat(provider): forward cursorParams to Cursor SDK model params

[breath57]

What

Adds an optional cursorParams field that flows from the opencode request body into Cursor SDK model.params, so per-model parameters (reasoning effort, fast mode, context size, thinking) become selectable from opencode.

Why

The Cursor SDK catalog already exposes per-model parameters, e.g.

• claude-opus-5: effort=[low|medium|high|xhigh|max], thinking=[false|true], context=[300k|1m], fast=[false|true]
• gpt-5.6-sol: reasoning=[none|low|medium|high|xhigh|max]
• composer-2.5: fast=[false|true]

and Agent.create({ model: { id, params: [{ id, value }] } }) accepts them (ModelSelection.params). Today the plugin drops all of it — the model id is carried as a plain string from the proxy to the runner.

How

cursorParams rides the same channel as the existing cursorModel field (opencode model options / variants.<name> → provider request body):

{
  "models": {
    "claude-opus-5": {
      "name": "Claude Opus 5",
      "options": { "cursorModel": "claude-opus-5", "cursorParams": "effort=high" },
      "variants": {
        "max": { "cursorParams": "effort=max,fast=true" }
      }
    }
  }
}

Accepted forms (normalized to [{ id, value }]):

• "effort=high,fast=true" (comma/space separated k=v pairs)
• JSON string: '[{"id":"effort","value":"high"}]'
• array of { id, value }
• plain object: { "effort": "high" }

Implementation (4 layers, minimal diff):

• src/provider/boundary.ts — new pure resolveRuntimeParams() (tested)
• src/plugin.ts — read body.cursorParams at both handler sites
• src/client/sdk-child.ts — carry params in the NDJSON request (only when non-empty)
• scripts/sdk-runner.mjs — buildModelSelection() → model: { id, params }

Compatibility

• No cursorParams present → byte-for-byte identical behavior to today
• Older runner + newer plugin: the extra field is ignored
• cursor-agent backend: params are not representable there and are ignored

Tests

• Unit: all accepted forms, invalid/empty → undefined, dedupe last-wins; NDJSON payload presence/absence; runner model-selection building
• E2E (real API, SDK backend): the same request with and without params both complete (exitCode=0, done=true, no error events)

Notes

• The plugin only forwards parameters; valid ids/values come from Cursor.models.list() (parameters per model, plus preset variants).
• Follow-up (not in this PR): auto-generating opencode variants from catalog parameters, and documenting the parameter matrix.

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Re-submission note

This is a re-submission: the previous PR (#130) was closed pending local verification on real hardware. GitHub refuses to reopen it (state cannot be changed — the branch was force-pushed or recreated), so a new PR is opened from the same branch. Branch content is unchanged (1 commit ahead of main, 0 behind). Now verified locally before submitting.

[Nomadcxx]

Thanks mate for the PR. The plugin now forwards OpenCode’s per-model settings to the Cursor SDK through cursorParams. Unit and integration checks pass, and the real API check covers requests with and without params. Thanks again.

cheers, RAMA