<essential_principles>

Extensions are TypeScript modules that hook into GSD's runtime (built on pi). They export a default function receiving ExtensionAPI and use it to subscribe to events, register tools/commands/shortcuts, and interact with the session.

GSD extension paths (community/user-installed extensions):

• Global: ~/.pi/agent/extensions/*.ts or ~/.pi/agent/extensions/*/index.ts
• Project-local: .gsd/extensions/*.ts or .gsd/extensions/*/index.ts

Note: ~/.gsd/agent/extensions/ is reserved for bundled extensions synced from the gsd-pi package. Community extensions placed there are silently ignored by the loader.

The three primitives:

1. Events — Listen and react (pi.on("event", handler)). Can block tool calls, modify messages, inject context.
2. Tools — Give the LLM new abilities (pi.registerTool()). LLM calls them autonomously.
3. Commands — Give users slash commands (pi.registerCommand()). Users type /mycommand.

Non-negotiable rules:

• Use StringEnum from @gsd/pi-ai for string enum params (NOT Type.Union/Type.Literal — breaks Google's API)
• Truncate tool output to 50KB / 2000 lines max (use truncateHead/truncateTail from @gsd/pi-coding-agent)
• Store stateful tool state in details for branching support
• Check signal?.aborted in long-running tool executions
• Use pi.exec() not child_process for shell commands
• Check ctx.hasUI before dialog methods (non-interactive modes exist)
• Session control methods (waitForIdle, newSession, fork, navigateTree, reload) are ONLY available in command handlers — they deadlock in event handlers
• Lines from render() must not exceed width — use truncateToWidth()
• Use theme from callback params, never import directly
• Strip leading @ from path params in custom tools (some models add it)

Available imports:

</essential_principles>

Based on user intent, route to the appropriate workflow:

Building a new extension:

• "Create an extension", "build a tool", "I want to add a command" → workflows/create-extension.md

Adding capabilities to an existing extension:

• "Add a tool to my extension", "add event hook", "add custom rendering" → workflows/add-capability.md

Debugging an extension:

• "My extension doesn't work", "tool not showing up", "event not firing" → workflows/debug-extension.md

If user intent is clear from context, skip the question and go directly to the workflow.

<reference_index> All domain knowledge in references/:

Core architecture: extension-lifecycle.md, events-reference.md API surface: extensionapi-reference.md, extensioncontext-reference.md Capabilities: custom-tools.md, custom-commands.md, custom-ui.md, custom-rendering.md Patterns: state-management.md, system-prompt-modification.md, compaction-session-control.md Infrastructure: model-provider-management.md, remote-execution-overrides.md, packaging-distribution.md, mode-behavior.md Spec: docs/extension-sdk/manifest-spec.md — manifest format, tiers, validation Testing: docs/extension-sdk/testing.md — mock patterns, test conventions SDK: docs/extension-sdk/ — the authoritative GSD-2 extension guide Gotchas: key-rules-gotchas.md </reference_index>

<workflows_index>

<success_criteria> Extension is complete when:

• extension-manifest.json exists with accurate provides listing all registered tools/commands/hooks/shortcuts
• TypeScript compiles without errors (jiti handles this at runtime)
• Extension loads on GSD startup or /reload without errors
• Tools appear in the LLM's system prompt and are callable
• Commands respond to /command input
• Event hooks fire at the expected lifecycle points
• Custom UI renders correctly within terminal width
• State persists correctly across session restarts (if stateful)
• Output is truncated to safe limits (if tools produce variable output) </success_criteria>