Add remote session loading

docs/internal/artifacts.md

@@ -16,6 +16,7 @@ Outputs:
 - resolved artifact path + provenance (`ResolvedSessionArtifact`);
 - runtime catalog entries for built-ins and configured artifacts;
 - requirement sets for canonical previous-session inputs.
+- canonical S3 session, run, current, session config, audio, and promoted artifact keys.
 
 ## Boundaries
 Owns:
@@ -43,6 +44,14 @@ Does not own:
 - configured artifact: `narratio.artifact.<artifact_key>`
 - canonical previous-session artifact: `narratio.previous_session.artifact.<artifact_key>`
 
+## S3 key helpers
+- session prefix: `{root_prefix}/campaigns/{campaign}/sessions/{session_id}/`
+- session config: `{session_prefix}/session.yml`
+- run prefix: `{session_prefix}/runs/{run_id}/`
+- audio prefix: `{session_prefix}/{session.inputs.audio_s3.prefix}`
+- current manifest: `{session_prefix}/current/manifest.json`
+- current run pointer: `{session_prefix}/current/run_id.txt`
+
 ## Runtime catalog model
 Catalog entries track:
 - `planned`: source is registered for this run;

docs/internal/stage-prepare.md

@@ -11,6 +11,7 @@ Prepare owns:
 ## Inputs and outputs
 Inputs:
 - resolved config/campaign/session (`pipeline.yml`, `campaign.yml`, `session.yml`);
+- remote session provenance when `session.yml` was loaded from S3;
 - campaign or session input files (`speakers`, `autocorrect`, `glossary`);
 - audio source:
   - local: `session.inputs.audio_dir` or `session.inputs.audio_files`;
@@ -72,6 +73,7 @@ Does not own:
 ## State and manifest behavior
 - Ensures workspace layout exists.
 - Materializes canonical input files and audio files.
+- Records `inputs/session.yml` provenance as local `session_config` or remote `session_config.s3`.
 - Resolves campaign-provided stable input paths relative to `campaign.yml`.
 - Resolves session-provided stable input overrides relative to `session.yml`.
 - Scans enabled configured artifact inputs for canonical sources:

docs/internal/storage.md

@@ -6,7 +6,7 @@ Document Narratio's remote storage backend contracts and implementations under `
 ## Inputs and outputs
 Inputs:
 - Resolved storage config (`pipeline.storage.*`).
-- Bucket-relative object keys and local file paths from stage/app orchestration.
+- Bucket-relative object keys and local file paths from app/stage orchestration.
 
 Outputs:
 - Listed/downloaded/uploaded object metadata (`ObjectInfo`).
@@ -57,6 +57,7 @@ Implementations:
 - `S3Backend` constructor fails when required bucket is missing or AWS client setup fails.
 - CRUD operations return contextual errors (including not-found behavior via `Exists`).
 - Key normalization is applied before operations (`\\` to `/`, leading slash trimmed).
+- Remote session loading uses `List` to find the exact `session.yml` key and `Download` to materialize it to a local temp file.
 
 ## Tests to inspect before changing
 - `internal/adapters/storage/factory_test.go`