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, structured run reports, summaries, coordination, and notification handoff.

## Inputs and outputs

`Run` accepts a context, optional config path, dry-run flag, force flag, stdout writer, output format, and optional notifier. It loads YAML config, discovers source bundles for each configured pipeline, plans each destination independently, optionally executes publish plans, builds a `RunReport`, projects that report to text or JSON when stdout is supplied, and returns an aggregated error if any destination fails.

`RunPipeline` accepts a context, config path, pipeline ID, dry-run flag, force flag, and optional notifier. It runs exactly one configured pipeline and returns the same `RunReport` model without writing command output. Unknown pipeline IDs return `PipelineNotFoundError`, detectable with `IsPipelineNotFound`.

`PipelineRunCoordinator` wraps `RunPipeline` with in-memory admission control. It returns `PipelineRunRecord` values containing run ID, pipeline ID, status, timestamps, report, and error text. Duplicate in-flight runs for the same pipeline ID return `DuplicatePipelineRunError`, detectable with `IsDuplicatePipelineRun`.

`Validate` and `Inspect` accept either a local path or one configured pipeline source. `Validate` discovers and validates bundles. `Inspect` writes bundle metadata and manifest file entries to stdout when provided.

## Run flow

The all-pipeline 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. selects source bundles for each destination according to destination path mapping;
5. opens each destination backend independently;
6. builds publish plans for the selected bundle and destination combinations;
7. records warnings, action records, output metadata, and summary counters in a `RunReport`;
8. executes publish or replacement plans unless dry-run is enabled;
9. invokes the notifier after successful publish or replacement actions;
10. projects the completed report to text or JSON output.

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.

`RunPipeline` uses the same config loading, secret loading, backend factory, transform registry, warning generation, destination planning, publish execution, notification behavior, and failure aggregation as `Run`, but first narrows the loaded config to the requested pipeline.

## Run implementation

`run.go` contains the public `Run` and `RunPipeline` entrypoints and the main configuration orchestration paths. Package-local run helpers are grouped by responsibility:

- `run_selection.go`: destination bundle selection, path mapping decisions, and fixed-path warnings;
- `run_warnings.go`: secret and SSH warning data;
- `run_output.go`: `RunReport`, action/output records, and text/JSON report projection;
- `run_summary.go`: summary counters and JSON summary records;
- `run_failures.go`: destination failure aggregation and partial-result detection;
- `run_notify.go`: notification event projection and action filtering.
- `run_coordinator.go`: in-memory single-pipeline run admission, run IDs, status records, and duplicate-run errors.

These helpers remain in `internal/app` because command output, warning collection, destination failure aggregation, notifier handoff, and backend construction are app-owned orchestration concerns.

## Run coordination

`PipelineRunCoordinator` keeps active run state in memory only. It allows different pipeline IDs to run concurrently and rejects a second active run for the same pipeline ID. Active state is cleared after success, destination-scoped failure, source/config failure, unknown pipeline ID, or context cancellation.

The admission context is checked before a run is admitted. Once admitted, execution uses the coordinator lifetime context so future transport request cancellation can stop waiting for admission without owning the actual run lifetime.

## Backend and transform wiring

The app-level backend factory registers local, SSH, and S3 backends for execution. Source and destination backend config is converted through a shared app-local open spec before adapter construction. S3 explicit credential references are resolved through the config environment resolver.

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, perform forced prefix deletion, or notify.

## Failure behavior

`Run` returns immediately for config loading errors, context cancellation before work starts, source open errors, and source discovery errors. `RunPipeline` also returns immediately with `PipelineNotFoundError` when the requested pipeline ID is not configured. 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.

Coordinator duplicate-run errors are admission errors and do not start, queue, or persist a run.

## 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.

Configured-source `Validate` and `Inspect` share source backend construction with `Run` and do not open destinations.

`PipelineRunCoordinator` is an app-layer concurrency boundary only. It does not persist run records, expose HTTP routes, or define transport status endpoints.

## 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.
- Destination-scoped failures still produce a structured report plus an aggregated error.
- Dry-run must not mutate destination storage or invoke notifications.
- `RunPipeline` must use the same core run path as `Run` after pipeline selection.
- Duplicate in-flight runs are rejected only for the same pipeline ID; different pipeline IDs may run concurrently.
- Concrete backend and transform registration stays at the app layer.
- The default notifier is `notify.Noop`.