feat(web): support ssh owner repo clone flow

- Add SSH-only owner/repo clone path for git.commumedia.org
- Preflight remote repository existence with git ls-remote before cloning
- Keep advanced URL paste fallback and blank repository creation
- Add focused backend and frontend coverage plus docs updates

Quality gates: python -m py_compile, vitest run src/components/repositories-settings-tab.test.tsx, npm run typecheck

openspec/changes/git-repo-ssh-clone-check/.openspec.yaml

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+schema: spec-driven
+created: 2026-05-22

openspec/changes/git-repo-ssh-clone-check/design.md

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+## Context
+
+The current repository creation flow already supports cloning remote repositories via `remote_url` and can normalize pasted browser URLs. However, the UI asks for a full URL, which is awkward for the fixed provider `git.commumedia.org`. The requested behavior is to enter `owner` and `repo`, check whether the repository exists, and clone only if it does.
+
+## Goals / Non-Goals
+
+**Goals:**
+- Accept SSH-only `owner` and `repo` inputs for cloning from `git.commumedia.org`
+- Verify repository existence before clone
+- Preserve full URL paste as a fallback path
+- Preserve blank repository creation
+- Reuse the existing repository create endpoint and shared dialog
+
+**Non-Goals:**
+- Supporting multiple git providers
+- Adding a remote repository discovery API
+- Supporting HTTPS clone flow for the new structured path
+- Changing repository storage or clone behavior beyond preflight validation
+
+## Decisions
+
+**1. Provider assumption**
+- Hardcode `git.commumedia.org` for the structured clone path
+- Build SSH URLs as `git@git.commumedia.org:{owner}/{repo}.git`
+
+**2. Existence check**
+- Use `git ls-remote` on the constructed SSH URL before cloning
+- If the command fails, surface a repository-not-found/inaccessible error and do not clone
+
+**3. UI structure**
+- Keep the shared repository creation dialog as the single entry point
+- In clone mode, collect `owner` and `repo` instead of asking for a full URL
+- Keep an advanced paste-URL fallback for existing behavior and browser URL parsing
+- Keep blank repository creation available in the same dialog
+
+**4. Backend behavior**
+- Reuse `POST /projects/{project_id}/repositories`
+- Add preflight logic before the existing `git clone --mirror`
+- Leave the database schema unchanged
+
+## Risks / Trade-offs
+
+**[Risk] SSH auth may still fail even if the repo exists** → Mitigation: preflight error should be explicit and user-facing.
+**[Risk] Command availability** → Mitigation: reuse the same `git` dependency already required for cloning.
+**[Risk] UI complexity** → Mitigation: keep the dialog shared and minimal, with fallback URL paste.

openspec/changes/git-repo-ssh-clone-check/proposal.md

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+## Why
+
+Repository creation already supports cloning from a remote URL, but the current UI only accepts a full URL. For the common fixed-provider case (`git.commumedia.org`), users should be able to enter `owner` and `repo` and have the app verify the repository exists before cloning. If the repository does not exist, the app should surface a clear error. Existing blank repository creation must remain available.
+
+## What Changes
+
+- Change the shared repository create dialog to support an SSH-only clone form with `owner` and `repo`
+- Build the clone target as `git@git.commumedia.org:{owner}/{repo}.git`
+- Preflight clone targets with `git ls-remote` before cloning
+- Return a clear error when the repository is missing or inaccessible
+- Keep the current full URL paste flow as an advanced fallback
+- Keep blank repository creation as a fallback option
+
+## Capabilities
+
+### Modified Capabilities
+
+- `git-repo`: Repository creation UX and clone validation reuse the existing create endpoint and clone path
+
+## Impact
+
+- Frontend: `repository-create-dialog.tsx`, `git-repositories.tsx`, `repositories-settings-tab.tsx`
+- Backend: `git_repositories.py` create endpoint clone preflight
+- Docs: repository creation guidance must reflect SSH-only owner/repo input
+- Tests: add coverage for SSH repo existence checks and fallback URL behavior

openspec/changes/git-repo-ssh-clone-check/tasks.md

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+## 1. Backend - SSH Existence Check
+
+- [ ] 1.1 Add `git ls-remote` preflight to repository creation in `git_repositories.py`
+- [ ] 1.2 Build SSH clone URL from `owner` and `repo` for `git.commumedia.org`
+- [ ] 1.3 Return a clear error when the repository is missing or inaccessible
+
+## 2. Frontend - Structured Clone Form
+
+- [ ] 2.1 Update `RepositoryCreateDialog` clone mode to accept `owner` and `repo`
+- [ ] 2.2 Keep advanced full-URL paste flow and blank repository fallback
+- [ ] 2.3 Reuse the shared dialog from repository settings and repositories page
+
+## 3. Validation and Docs
+
+- [ ] 3.1 Update repository docs to explain SSH-only owner/repo input
+- [ ] 3.2 Add tests for success, missing repo, and URL fallback behavior
+
+## 4. Quality Gates
+
+- [ ] 4.1 Run backend and frontend targeted tests
+- [ ] 4.2 Run frontend typecheck and lint where applicable
+- [ ] 4.3 Commit and push changes