Finish render rollout with markdown publish defaults, analyze guidance, and docs updates

docs/internal/stage-render.md

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+# Stage: render
+
+## Purpose
+Render Markdown transcript artifacts from normalized JSON transcripts via Seriatim.
+
+## Inputs
+- `narratio.transcript.final` (`transcripts/final.json`)
+- `narratio.transcript.final_trimmed` (`transcripts/final.trimmed.json`)
+
+## Outputs
+- `narratio.transcript.final_markdown` -> `transcripts/final.md`
+- `narratio.transcript.final_trimmed_markdown` -> `transcripts/final.trimmed.md`
+
+## Key Behavior
+- uses `pipeline.render` settings (enabled/format/title/booleans).
+- resolves inputs manifest-first, then canonical fallback.
+- writes run-local outputs first, then materializes canonical session outputs.
+- records input provenance, output paths, adapter metadata, logs, and generated config refs.
+- skips with stage metadata when `pipeline.render.enabled=false`.
+
+## Failure Semantics
+- missing normalized input fails with normalize rerun guidance.
+- missing trimmed input fails with trim rerun guidance.
+- adapter/subprocess failure fails stage.
+- empty render output files fail validation.
+
+## Invariants
+- only `format: markdown` is supported.
+- render stage owns production of built-in Markdown transcript sources.