Add output schema registry and public contract docs

docs/architecture.md

@@ -216,8 +216,27 @@ Additional checks:
 - duplicate explicit source IDs are rejected.
 
 ### Transcript output
-Current output uses `schema.TranscriptToJSON` and is a bare JSON array of normalized segments:
-- `id`, `speaker`, `start`, `end`, `text`, optional `categories`.
+Transcript output is selected through an output schema registry (`internal/core/outputschema`).
+
+Supported output schemas:
+- `bare-segments` (default):
+  - top-level JSON array of normalized segments;
+  - each segment includes `id`, `speaker`, `start`, `end`, `text`, optional `categories`.
+- `audita-v1`:
+  - top-level object with:
+    - `schema: "audita-v1"`
+    - `version: "v1"`
+    - `segments: [...]` (same normalized segment payload).
+
+Current status:
+- `seriatim-intermediate` is not implemented yet; selecting it fails clearly as an unsupported output schema.
+
+Selection behavior:
+- CLI: `--output-schema <name>`
+- file config: `output.schema: <name>`
+- precedence remains runtime-wide defaults -> file config -> env -> CLI.
+
+Both stdout transcript output and `--output` file output use the same selected output encoder.
 
 ### Glossary input
 YAML with `glossary` entries. Required fields per entry:
@@ -544,6 +563,15 @@ Current process reports also include:
 - run-level module summary totals and failed module instance metadata.
 - module-level validator decisions and validator rejections.
 - optional decision-level diagnostic artifact paths for validator LLM interactions when available.
+- explicit report metadata:
+  - report schema name;
+  - report schema version;
+  - selected output schema;
+  - config file version when config file input is used.
+
+Current report schema metadata values:
+- `report_metadata.report_schema_name = "audita-process-report"`
+- `report_metadata.report_schema_version = "v1"`
 
 Retention modes implemented in `ApplyRetention`:
 - `always`: keep all run directories.
@@ -588,6 +616,10 @@ The runtime now includes hardened subprocess behavior for parent-process callers
 - retained failure diagnostics (`report.json`, `error.log`, and artifacts written before failure);
 - deterministic timeout/cancellation behavior in tests;
 - redaction coverage for API keys/secrets across reports, diagnostics artifacts, and surfaced errors.
+- stable output routing behavior:
+  - with `--output`, stdout remains empty on success;
+  - without `--output`, stdout contains only transcript JSON in the selected output schema;
+  - `--report-json` writes report data to file only (never stdout).
 
 Operational caller guidance is documented in [`docs/subprocess-operations.md`](docs/subprocess-operations.md).