docs(changes): propose gemini cli slash support

openspec/changes/add-gemini-cli-slash-commands/proposal.md

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+## Why
+Gemini CLI now supports project-scoped custom slash commands that live under `.gemini/commands`. Teams using OpenSpec with Gemini CLI must currently hand-write these TOML files to stay aligned with the proposal/apply/archive workflow, creating drift and inconsistent instructions. Extending OpenSpec's automation keeps Gemini CLI users at parity with Claude, Cursor, and OpenCode.
+
+## Research Findings
+- Gemini CLI discovers user and project commands from `~/.gemini/commands/` and `<project>/.gemini/commands/`, with project commands winning on name conflicts. Commands are named from their relative path (e.g., `openspec/proposal.toml` → `/openspec:proposal`).
+- Each command definition is a TOML file that must provide a `prompt` string and can optionally include a `description`. Multiline prompts use triple quotes and safely support argument injection via `{{args}}` as well as shell execution blocks (`!{...}`) that trigger confirmations.
+- Gemini CLI loads these definitions through `FileCommandLoader`, which scans both command directories, parses TOML via Zod, and adapts them into executable slash commands at runtime.
+
+## What Changes
+- Treat Gemini CLI as a first-class slash command target during `openspec init`, generating `.gemini/commands/openspec/proposal.toml`, `apply.toml`, and `archive.toml` populated from shared templates wrapped with OpenSpec markers.
+- Refresh existing Gemini CLI command files during `openspec update`, updating only the marker-managed prompt content when the files already exist.
+- Add a Gemini CLI option to the AI tool selection UI and to the slash command registry so users can configure or refresh it alongside other assistants.
+- Provide Vitest coverage that mirrors existing slash command tests for creation and update flows, ensuring the TOML scaffolding integrates cleanly with FileCommandLoader expectations.
+- Document the Gemini CLI slash command behavior in the relevant specs so downstream automation and teams understand the new capability.
+
+## Impact
+- Affected specs: `cli-init`, `cli-update`
+- Affected code (planned): slash command configurators/registry, CLI init & update flows, template management, AI tool configuration prompts
+- Affected tests: `test/core/init.test.ts`, `test/core/update.test.ts` (new cases for Gemini CLI)

openspec/changes/add-gemini-cli-slash-commands/specs/cli-init/spec.md

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+## MODIFIED Requirements
+### Requirement: Slash Command Configuration
+The init command SHALL generate slash command files for supported editors using shared templates.
+
+#### Scenario: Generating slash commands for Gemini CLI
+- **WHEN** the user selects Gemini CLI during initialization
+- **THEN** create `.gemini/commands/openspec/proposal.toml`, `.gemini/commands/openspec/apply.toml`, and `.gemini/commands/openspec/archive.toml`
+- **AND** populate each file from shared templates so command text matches other tools
+- **AND** ensure each TOML file contains OpenSpec-managed markers around the prompt so future updates can refresh the body safely

openspec/changes/add-gemini-cli-slash-commands/specs/cli-update/spec.md

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+## MODIFIED Requirements
+### Requirement: Slash Command Updates
+The update command SHALL refresh existing slash command files for configured tools without creating new ones.
+
+#### Scenario: Updating slash commands for Gemini CLI
+- **WHEN** `.gemini/commands/openspec/` contains `proposal.toml`, `apply.toml`, and `archive.toml`
+- **THEN** refresh each file using shared templates while preserving content outside the OpenSpec markers
+- **AND** ensure the updated prompts remain wrapped with markers to support future refreshes

openspec/changes/add-gemini-cli-slash-commands/tasks.md

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+## 1. Slash command scaffolding
+- [ ] 1.1 Add a Gemini CLI entry to the slash command registry with a `GeminiSlashCommandConfigurator` that maps `proposal`, `apply`, and `archive` to `.gemini/commands/openspec/*.toml`.
+- [ ] 1.2 Reuse existing slash command templates for the prompt bodies and ensure they are wrapped by OpenSpec markers inside the TOML `prompt` string.
+- [ ] 1.3 Define any Gemini-specific metadata (e.g., `description` values) that should live alongside the prompts to improve `/help` readability.
+
+## 2. CLI init integration
+- [ ] 2.1 Extend the AI tool selection options to list Gemini CLI as supporting OpenSpec slash commands, including already-configured detection and success messaging.
+- [ ] 2.2 Ensure `openspec init` writes the Gemini CLI TOML files when the tool is selected, creating parent directories as needed.
+
+## 3. CLI update integration
+- [ ] 3.1 Update the slash command refresh flow so `openspec update` rewrites Gemini CLI TOML prompts only when the files already exist.
+- [ ] 3.2 Extend logging to report Gemini slash command updates alongside other tools.
+
+## 4. Tests
+- [ ] 4.1 Add Vitest coverage under `test/core/init.test.ts` that verifies the Gemini CLI TOML files are generated with the expected prompts and markers.
+- [ ] 4.2 Add Vitest coverage under `test/core/update.test.ts` that confirms existing Gemini TOML files get refreshed while preserving content outside the markers.
+
+## 5. Documentation & polish
+- [ ] 5.1 Update README (or other user-facing docs) to mention Gemini CLI slash command support and how the generated files map to `/openspec:*` commands.
+- [ ] 5.2 Document any Gemini-specific limitations or follow-up work (e.g., handling of folder trust) if discovered during implementation.