Move documentation for external integrations into the docs/integrations subfolder

docs/integrations/seriatim.md

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+# Integration: seriatim
+
+## Purpose
+Define Narratio's adapter contract for merge, normalize, and trim subprocess invocations of Seriatim.
+
+## Inputs and Outputs
+Inputs:
+- `MergeRequest`: raw/normalized transcript inputs, output path, optional report, speaker/autocorrect paths, logs/config
+- `NormalizeRequest`: input transcript, output path, schema, optional report, timeout/log/config
+- `TrimRequest`: input transcript, output path, keep selector, timeout/log/config
+
+Outputs:
+- `MergeResult`, `NormalizeResult`, `TrimResult` with output paths, logs/config paths, exit code, duration, binary provenance, and metadata.
+
+## Boundaries
+Owns:
+- Validated deterministic CLI invocation construction
+- Optional env tuning propagation for merge
+- Invocation config file emission
+- JSON output validation
+
+Does not own:
+- Transcript input selection/promotion logic (stage-owned)
+- Bounds computation (scriptorium/trim-stage-owned)
+
+## Config Fields Used
+Via `pipeline.seriatim.*` mapped in app/stage wiring:
+- `binary`, `timeout`, `output_schema`, `coalesce_gap`, `report`
+- `env.overlap_word_run_gap`
+- `env.overlap_word_run_reorder_window`
+- `env.backchannel_max_duration`
+- `env.filler_max_duration`
+
+## External Adapters Used
+- Shared subprocess helper (`internal/adapters/subprocess`).
+
+## State and Manifest Behavior
+- No direct manifest writes.
+- Stage metadata consumes adapter result fields and preserves generated config/log references.
+
+## Skip and Resume Behavior
+- Adapter has no skip/resume logic. Runner controls stage execution.
+
+## Failure Behavior
+- Constructor fails for invalid binary/timeout/output-schema/coalesce-gap.
+- Merge fails on missing output path/inputs/report path (if enabled), subprocess errors, invalid merged output JSON, invalid report JSON.
+- Normalize fails on missing input/output, invalid schema, subprocess errors, invalid normalized output JSON shape, invalid report JSON.
+- Trim fails on missing input/output/keep selector, subprocess errors, invalid trimmed output JSON shape.
+
+## Tests to Inspect Before Changing
+- `internal/adapters/seriatim/subprocess_test.go`
+- `internal/adapters/seriatim/fake_test.go`
+- `internal/stage/merge_test.go`
+- `internal/stage/normalize_test.go`
+- `internal/stage/trim_test.go`
+
+## Architectural Invariants
+- Supported output schemas are limited to `seriatim-minimal`, `seriatim-intermediate`, `seriatim-full`.
+- Normalize/trim outputs must include `segments` arrays.
+- Merge/normalize/trim all route through deterministic subprocess invocation.