distributor/docs/internal/app.md

Application Orchestration

Purpose

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.

Inputs and outputs

Run accepts a context, optional config path, dry-run 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.

Backend and transform wiring

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.

Dry-run behavior

Dry-run still loads config, opens backends, discovers bundles, inspects destinations, resolves transforms, and builds publish plans. It does not write destination outputs, write .distributor.json, delete managed outputs, or notify.

Failure behavior

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.

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.

Validate and Inspect are local path commands. Remote execution wiring currently belongs to Run.

Tests

Before changing app orchestration, inspect tests under:

• internal/app
• internal/cli
• internal/publish

Invariants

• One source fans out to each destination independently.
• Destination failures do not prevent later destinations from being planned.
• Dry-run must not mutate destination storage or invoke notifications.
• Concrete backend and transform registration stays at the app layer.
• The default notifier is notify.Noop.