fix(jsonrpc): read response before waiting

[qiz029]

What changed

• Decode the complete JSON-RPC response before calling Cmd.Wait.
• Preserve process termination and cleanup after the response is read.
• Add a regression test using a fast provider that writes a large valid response and exits immediately.

Root cause

Provider.call started Cmd.Wait in a goroutine before decoding StdoutPipe. Go closes the pipe when Wait completes, so a fast-exiting provider could race the decoder and produce read |0: file already closed even though it emitted a valid response.

Impact

JSON-RPC providers no longer fail nondeterministically when they exit quickly after writing a response. Timeout behavior remains controlled by exec.CommandContext.

Validation

• Regression test on old implementation: failed 9 of 10 runs with file already closed
• Regression test after fix: 100 of 100 runs passed
• Original CLI conformance test: 30 of 30 runs passed
• go test ./... -count=1
• go vet ./...
• golangci-lint fmt --diff
• scripts/check-production-complexity.sh
• Product coverage: 78.1% (required 75%)

Local golangci-lint run was blocked by a broken local Go toolchain (go1.26.4 loading no packages; the cached Go 1.25 toolchain is missing unsafe). GitHub Actions provides the clean Go 1.25 lint result.

[Copilot]

Pull request overview

This PR fixes a JSON-RPC stdio race where calling Cmd.Wait() too early could close StdoutPipe while the response decoder was still reading, causing nondeterministic failures for fast-exiting providers. The fix ensures the full JSON-RPC response is decoded before waiting, and adds a regression test that reproduces the prior failure mode with a large, valid response.

Changes:

• Reorder process lifecycle in Provider.call to decode stdout fully before invoking cmd.Wait().
• Preserve cleanup behavior by still terminating the provider process after reading the response.
• Add a regression test using a helper provider mode that emits a large response and exits immediately.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
internal/adapters/jsonrpc/provider.go	Decodes the JSON-RPC response before cmd.Wait() to avoid StdoutPipe being closed mid-decode.
internal/adapters/jsonrpc/provider_test.go	Adds a regression test and helper mode producing a large fast response to validate the race fix.

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