`internal/app` owns top-level use cases for `run`, `validate`, and `inspect`. It wires configuration, storage backends, transforms, publish planning, execution, summaries, and notification handoff.
`Run` accepts a context, optional config path, dry-run flag, force flag, stdout writer, and optional notifier. It loads YAML config, discovers source bundles for each configured pipeline, plans each destination independently, optionally executes publish plans, writes summary output when stdout is supplied, and returns an aggregated error if any destination fails.
`Validate` and `Inspect` accept a local path. `Validate` discovers and validates bundles. `Inspect` writes bundle metadata and manifest file entries to stdout when provided.
## Run flow
The runner:
1. loads config from the supplied path or `config.DefaultConfigPath`;
2. opens the configured source backend;
3. discovers validated bundles from the source root;
4. opens each destination backend independently;
5. builds a publish plan for each bundle and destination;
6. prints plan lines and records summary counters;
7. executes publish or replacement plans unless dry-run is enabled;
8. invokes the notifier after successful publish or replacement actions.
Destination failures are collected while later destinations continue to run. Source open and source discovery failures stop the run because there are no valid bundles to fan out.
The app-level backend factory registers local, SSH, and S3 backends for execution. S3 explicit credential references are resolved through the config environment resolver before adapter construction.
The app-level transform registry registers Markdown-to-HTML using `internal/transform/markdown`. Lower-level publish code receives a resolver and does not import concrete transform implementations.
`Run` returns immediately for config loading errors, context cancellation before work starts, source open errors, and source discovery errors. Per-destination backend, planning, execution, and notification errors are aggregated into one run error after remaining destinations have been attempted.
Run diagnostics include pipeline id, destination id, destination backend, and bundle path for destination-scoped failures. Source open and discovery failures include the source backend.
Stdout write errors are returned immediately because the caller's requested output stream can no longer be trusted.
## Boundaries
`internal/app` coordinates packages but does not own manifest validation rules, destination state comparison, storage path rules, output planning, transform rendering, or backend-specific filesystem behavior.
