Add GitHub --app-set support to repos install

[ggallen]

What is missing

fullsend repos install does not support selecting the GitHub App set used by a repository. This prevents manifest-managed repositories from using the same custom app-set configuration supported by fullsend github setup.

The option is GitHub-specific. It should not affect GitLab installation behavior or GitLab manifest validation.

What should happen

Add GitHub app-set support to fullsend repos install:

• Add an --app-set command-line option.
• Add a manifest-level default in repos.yaml.
• Allow an individual repository entry to override that default.
• Resolve the effective value using the same precedence and override semantics as comparable repos install options.
• Persist the effective app-set value on the target GitHub repository in the same way as fullsend github setup, including the FULLSEND_APP_SET repository variable required by dispatch and fix workflows.
• Ensure reruns and convergence preserve and repair the effective value rather than silently replacing a custom value with the built-in default.
• Reject or ignore the option appropriately for GitLab instead of applying GitHub behavior to GitLab projects.

The app-set behavior should match fullsend github setup for the relevant GitHub application settings. Shared validation, resolution, and application-setting logic should be factored into common code wherever practical instead of being reimplemented separately in the two commands.

Precedence

Use the established repos install precedence model for scalar options, including the built-in default, manifest defaults, per-repository overrides, and command-line values where applicable. Document the exact precedence and any unset/disable sentinel behavior so it is consistent with other manifest-managed options.

Documentation and testing

Update the CLI reference, repository-management guides, and manifest/configuration documentation. Add tests covering:

• command-line, manifest-default, and per-repository values
• precedence and unset/override behavior
• the built-in default
• fresh install, rerun, and convergence
• repository-variable output and drift repair
• GitHub-only validation and GitLab behavior
• parity of app-set validation and application settings with fullsend github setup

The implementation must not weaken exact bot-identity matching or introduce wildcard bot recognition.

[fullsend-ai-triage]

🤖 Finished Triage · ✅ Success · Started 11:49 PM UTC · Completed 11:54 PM UTC

Commit: fa25e2e · View workflow run →

Runtime: claude · Model: sonnet → claude-sonnet-5 · Effort: high · Cost: $0.72

[fullsend-ai-triage]

This gap is confirmed in the current code: internal/cli/repos.go / internal/repos/install.go have no app-set flag, manifest field, or per-repo override at all, while internal/cli/github.go already supports --app-set end-to-end (validation via appsetup.ValidateAppSet, threading through runAppSetup). No open PR or issue currently implements this, and issue #7318 (deprecating github setup in favor of repos install) is related context — closing this gap helps that deprecation reach feature parity — but is not itself a blocker.

A precedent for the requested precedence model already exists in internal/repos/manifest.go for other scalar options (e.g. mint_url, via resolveField and an unset sentinel), so implementation can follow that established pattern rather than inventing a new one.

One note for whoever picks this up: the repository variable named in the issue as required by "dispatch and fix workflows" doesn't appear to be read by any current scaffold workflow YAML — comparable persisted variables (e.g. FULLSEND_REVIEW_CLIENT_ID) are likewise only written/read back by Go-side install/converge/probe code, not referenced in workflow files. Worth confirming the intended consumer before assuming workflow-file changes are needed — current evidence suggests this is Go-side only.

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Labels: Matches the established convention for install-related feature requests in this repo (component/install + type/feature, with feature for human-prioritization queuing, as seen on similar issues like #7631 and #7749).

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Next steps:

• /fs-code — agent creates a PR to implement this issue
• /fs-code <your instruction> — agent implements with your specific guidance

[ggallen]

/fs-code

[fullsend-ai-coder]

🤖 Finished Code · ✅ Success · Started 12:07 AM UTC · Completed 1:08 AM UTC

Commit: 114478f · View workflow run →

Runtime: pi · Model: xai/grok-4.6 · Effort: high · Cost: $2.64

[fullsend-ai-coder]

ℹ️ No PR created — agent determined no changes needed

The code agent ran and evaluated issue #7882, but did not produce changes to submit as a pull request.

Reason: No changed files in agent's commit(s)

Workflow run: https://github.com/fullsend-ai/fullsend/actions/runs/36794377821

Retry with /fs-code if appropriate.

[ggallen]

/fs-code

Implement only the smallest useful slice of issue #7882 and create a PR.

Add a GitHub-only --app-set flag to fullsend repos install.

For this PR:

• Default it to fullsend-ai.
• Validate it with the existing appsetup.ValidateAppSet.
• Thread the value through the install path.
• For GitHub repositories, persist it as the FULLSEND_APP_SET repository variable.
• Add focused tests for the default, custom value, invalid value, and GitHub-only behavior.
• Update the repos install CLI documentation.
• Do not implement repos.yaml defaults, per-repository overrides, precedence rules, shared app-setup refactoring, or full application-set
  ting parity yet.
• Do not modify any files under .github/workflows/ or any generated workflow.
• Do not modify GitLab behavior.

Keep the change small and self-contained. Run focused tests, formatting, and the relevant Go checks, then commit and create the PR.

[fullsend-ai-coder]

🤖 Finished Code · ✅ Success · Started 1:14 AM UTC · Completed 2:15 AM UTC

Commit: 114478f · View workflow run →

Runtime: pi · Model: xai/grok-4.6 · Effort: high · Cost: $0.43

[fullsend-ai-coder]

ℹ️ No PR created — agent determined no changes needed

The code agent ran and evaluated issue #7882, but did not produce changes to submit as a pull request.

Reason: Agent did not create a feature branch (current: 'main')

Workflow run: https://github.com/fullsend-ai/fullsend/actions/runs/36799964570

Retry with /fs-code if appropriate.

[ggallen]

/fs-code

Create a PR with only the documentation changes for this issue. Do not include any other changes.

[fullsend-ai-coder]

🤖 Code · Started 2:23 AM UTC

Commit: 114478f · View workflow run →