feat(cmd): add JSON result envelope on stdout for up/build/exec

[skevetter]

Summary

Adds structured JSON result output to up, build, and exec commands matching the official devcontainer CLI envelope format ({"outcome":"success","containerId":"...","remoteUser":"...","remoteWorkspaceFolder":"..."}).

• up and build emit the envelope to stdout on success (error envelope on failure)
• exec emits to stderr since stdout is reserved for the executed command's output
• Includes unit tests for envelope marshaling with edge cases

Summary by CodeRabbit

Release Notes

• New Features

  • CLI commands now output structured JSON responses, including container ID, remote user, and workspace information on success and detailed error messages on failure, enabling better programmatic integration and automation.

• Tests

  • Added comprehensive test coverage for JSON output formatting and validation.

[netlify]

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[coderabbitai]

Caution

Review failed

The pull request is closed.

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: ad01a959-cac8-49ab-8737-97abb559061a

📥 Commits

Reviewing files that changed from the base of the PR and between d396b6b and 9e9103c.

📒 Files selected for processing (5)

• cmd/build.go
• cmd/exec.go
• cmd/up.go
• pkg/devcontainer/config/envelope.go
• pkg/devcontainer/config/envelope_test.go

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📝 Walkthrough

Walkthrough

The PR introduces standardized JSON output envelopes for structured success and error responses across multiple CLI commands. A new envelope.go file defines the envelope types and JSON writer helpers, which are then integrated into the build, exec, and up command handlers to emit structured results to their respective output streams.

Changes

JSON Output Envelope System

Layer / File(s)	Summary
Data Shape pkg/devcontainer/config/envelope.go	New ResultEnvelope struct with Outcome, ContainerID, RemoteUser, and RemoteWorkspaceFolder fields; new ErrorEnvelope struct with Outcome and Message fields.
Core Implementation pkg/devcontainer/config/envelope.go	WriteResultJSON marshals a success envelope and writes it with trailing newline; WriteErrorJSON marshals an error envelope and writes it with trailing newline. Both return any JSON marshal or I/O errors.
Command Integration cmd/build.go, cmd/exec.go, cmd/up.go	Each command now captures execution results and errors, then calls the appropriate envelope writer to emit JSON to os.Stdout (build, up) or os.Stderr (exec) before returning. Success paths extract containerID, remoteUser, and workdir from execution context.
Tests & Verification pkg/devcontainer/config/envelope_test.go	Table-driven tests validate WriteResultJSON and WriteErrorJSON output structure, JSON parseability, field values, newline termination, and single-line formatting.

Sequence Diagram

sequenceDiagram
participant User
participant Command as Build/Exec/Up Command
participant Executor as Execution Handler
participant Envelope as JSON Envelope Writer
participant Output as os.Stdout/stderr
User->>Command: Execute command with args
Command->>Executor: Execute (BuildAgent, execInContainer, etc.)
alt Execution succeeds
Executor-->>Command: result, nil
Command->>Command: Extract containerID, user, workdir
Command->>Envelope: WriteResultJSON(output, containerID, user, workdir)
Envelope->>Envelope: Marshal ResultEnvelope{Outcome: "success", ...}
Envelope->>Output: Write JSON + newline
Envelope-->>Command: nil
Command-->>User: success
else Execution fails
Executor-->>Command: nil, error
Command->>Envelope: WriteErrorJSON(output, error.Error())
Envelope->>Envelope: Marshal ErrorEnvelope{Outcome: "error", Message: msg}
Envelope->>Output: Write JSON + newline
Envelope-->>Command: error
Command-->>User: error
end

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Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related PRs

• feat(cli): add exec command for container command execution #157: Adds the exec command; this PR modifies ExecCmd.Run to emit JSON responses, so changes to the same command flow logic.
• feat(exec): add devcontainer spec compliance (workdir, user, remoteEnv, userEnvProbe) #161: Modifies cmd/exec.go and the handling of ExecCmd.Run behavior, producing exec results and workspace context similarly to this PR.

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