diff --git a/README.md b/README.md
index b8b6043..667031e 100644
--- a/README.md
+++ b/README.md
@@ -28,7 +28,12 @@ go run ./cmd/seriatim merge \
 - Operations guide: [docs/operations.md](docs/operations.md)
 - Troubleshooting: [docs/troubleshooting.md](docs/troubleshooting.md)
 - Development architecture policy: [docs/policy/architecture.md](docs/policy/architecture.md)
+- Contributor workflow: [docs/policy/development.md](docs/policy/development.md)
 - Documentation policy: [docs/policy/documentation.md](docs/policy/documentation.md)
+- Internal implementation docs:
+  - [docs/internal/pipeline.md](docs/internal/pipeline.md)
+  - [docs/internal/artifacts.md](docs/internal/artifacts.md)
+  - [docs/internal/modules.md](docs/internal/modules.md)
 - Public JSON schemas:
   - [schema/minimal-output.schema.json](schema/minimal-output.schema.json)
   - [schema/intermediate-output.schema.json](schema/intermediate-output.schema.json)
diff --git a/docs/internal/artifacts.md b/docs/internal/artifacts.md
new file mode 100644
index 0000000..421b7a8
--- /dev/null
+++ b/docs/internal/artifacts.md
@@ -0,0 +1,140 @@
+# Artifact Internals
+
+## Purpose
+
+Describes public artifact conversion and validation internals for merge output,
+trim, and normalize.
+
+## Artifact contracts
+
+Public contracts live in `schema/`:
+
+- full: `schema.Transcript`
+- intermediate: `schema.IntermediateTranscript`
+- minimal: `schema.MinimalTranscript`
+
+Machine-readable schemas:
+
+- `schema/full-output.schema.json`
+- `schema/intermediate-output.schema.json`
+- `schema/minimal-output.schema.json`
+
+## Schema selection
+
+Merge pipeline conversion uses `internal/artifact.SelectedFromMerged`:
+
+- `seriatim-full` -> `artifact.FromMerged`
+- `seriatim-intermediate` -> `artifact.IntermediateFromMerged`
+- `seriatim-minimal` -> `artifact.MinimalFromMerged`
+
+Unknown/empty selection falls back to intermediate conversion.
+
+## Merge conversion behavior
+
+`internal/artifact` converts `model.MergedTranscript` to public contracts:
+
+- full schema preserves source/provenance, overlap groups, and metadata module
+  lists.
+- intermediate schema emits segment timing/text/speaker with optional
+  categories and compact metadata.
+- minimal schema emits compact segment timing/text/speaker and compact
+  metadata.
+
+## Validation behavior
+
+`schema/output.go` validates both structure and semantics:
+
+- embedded JSON Schema validation via `jsonschema/v6`
+- semantic checks for sequential segment IDs starting at `1`
+- semantic checks for non-inverted segment timing (`end >= start`)
+- full schema overlap-group timing checks (`group.end >= group.start`)
+
+## Trim internals
+
+`internal/trim` is artifact-level projection, not merge reprocessing.
+
+Core flow:
+
+1. Parse selector (`internal/trim/selector.go`).
+2. Parse input artifact and detect schema (`ParseArtifactJSON`).
+3. Apply keep/remove projection with sequential ID renumbering.
+4. Recompute overlap groups only for full-schema artifacts.
+5. Optionally convert output schema when supported.
+6. Validate output artifact before write.
+
+Schema-conversion limits:
+
+- full -> intermediate/minimal supported.
+- intermediate -> minimal supported.
+- minimal -> intermediate supported.
+- intermediate/minimal -> full is rejected.
+
+Trim invariants:
+
+- selected IDs must exist in input.
+- input IDs must be positive, unique, sequential.
+- retained order follows input transcript order.
+- output IDs are reassigned to `1..N`.
+
+## Normalize internals
+
+`internal/normalize` canonicalizes transcript-like JSON input into a selected
+public schema.
+
+Parse layer (`parse.go`):
+
+- accepts object-with-`segments` or bare segment array
+- repairs missing timing deterministically
+- swaps inverted timing
+- fills missing/blank speaker with `Unknown_Speaker`
+- drops missing/blank text segments
+
+Build layer (`build.go`):
+
+- sorts deterministically by `(start, end, input_index, speaker)`
+- reassigns output IDs sequentially
+- builds minimal/intermediate/full output shape
+- validates selected output schema before write
+
+Run layer (`normalize.go`):
+
+- writes output JSON
+- optionally writes report with `normalize-audit`
+
+Normalize invariant:
+
+- report events do not embed transcript text.
+
+## Boundaries
+
+- CLI flag semantics belong to `docs/cli.md`.
+- Runtime config/env surfaces belong to `docs/config.md`.
+- This doc describes internal conversion/validation behavior only.
+
+## Failure behavior
+
+Representative failure classes:
+
+- malformed or unsupported input JSON shape
+- schema validation failure for parsed artifact or built output
+- unsupported schema conversion path (trim)
+- selector or input-ID consistency errors (trim)
+- output/report file write failures from command paths
+
+## Tests to inspect before changes
+
+- `schema/output_test.go`
+- `internal/artifact/transcript_test.go`
+- `internal/trim/selector_test.go`
+- `internal/trim/artifact_test.go`
+- `internal/trim/apply_test.go`
+- `internal/normalize/parse_test.go`
+- `internal/cli/trim_test.go`
+- `internal/cli/normalize_test.go`
+
+## Invariants
+
+- Public artifacts are validated through `schema` before acceptance.
+- Segment IDs in emitted artifacts are sequential and deterministic.
+- Internal-only fields are not emitted in minimal/intermediate contracts.
+- Trim and normalize stay artifact-level and do not execute merge modules.
diff --git a/docs/internal/modules.md b/docs/internal/modules.md
new file mode 100644
index 0000000..98b5e21
--- /dev/null
+++ b/docs/internal/modules.md
@@ -0,0 +1,119 @@
+# Built-In Modules
+
+## Purpose
+
+Describes implemented built-in module behavior and boundaries in
+`internal/builtin`.
+
+## Implemented module set
+
+Input reader:
+
+- `json-files`
+
+Preprocessing:
+
+- `validate-raw`
+- `normalize-speakers`
+- `trim-text`
+
+Merger:
+
+- `chronological-merge`
+
+Postprocessing:
+
+- `detect-overlaps`
+- `resolve-overlaps`
+- `backchannel`
+- `filler`
+- `resolve-danglers`
+- `coalesce`
+- `autocorrect`
+- `assign-ids`
+- `validate-output`
+
+Output writer:
+
+- `json`
+
+## Inputs, outputs, and side effects
+
+- `json-files`: reads JSON files from `cfg.InputFiles`, parses supported
+  segment/word fields, emits warnings for untimed words.
+- `validate-raw`: validates raw source/timing invariants.
+- `normalize-speakers`: converts raw transcripts to canonical segments,
+  optionally resolving speakers from `cfg.SpeakersFile`.
+- `trim-text`: trims canonical segment text whitespace.
+- `chronological-merge`: flattens canonical segments and applies deterministic
+  sort (`model.SegmentLess`).
+- `detect-overlaps`: annotates overlap groups.
+- `resolve-overlaps`: rewrites overlap groups using timed words and thresholds.
+- `backchannel`/`filler`: classify short utterances using duration thresholds.
+- `resolve-danglers`: merges dangling derived fragments.
+- `coalesce`: merges adjacent same-speaker segments within configured gap.
+- `autocorrect`: applies YAML replacement rules when configured.
+- `assign-ids`: assigns final sequential IDs.
+- `validate-output`: validates selected public artifact shape.
+- `json`: writes artifact JSON to `cfg.OutputFile`.
+
+Filesystem side effects are limited to:
+
+- reading configured input/YAML files
+- writing configured output artifact
+
+## Config fields used
+
+Primary module inputs from `config.Config`:
+
+- file paths: `InputFiles`, `SpeakersFile`, `AutocorrectFile`, `OutputFile`
+- schema/modules: `OutputSchema`, `OutputModules`
+- overlap/coalesce thresholds: `OverlapWordRunGap`,
+  `WordRunReorderWindow`, `CoalesceGap`
+- category thresholds: `BackchannelMaxDuration`, `FillerMaxDuration`
+
+## Ordering constraints
+
+- Preprocessing must satisfy state contracts from `raw` to `canonical`.
+- Order-sensitive transforms should run before `assign-ids`.
+- `validate-output` should run after final ID assignment and output-shape
+  mutations.
+- Default configuration includes a second `detect-overlaps` pass after
+  transformations.
+
+## Boundaries
+
+- Modules implement behavior; CLI/config parsing remains outside modules.
+- Modules communicate through explicit model contracts and report events.
+- Output modules operate on final artifacts and do not re-run transform logic.
+
+## Failure behavior
+
+Representative failures:
+
+- invalid input JSON shape or typed field errors (`json-files`)
+- invalid YAML or unmatched speaker map entries
+- unknown module names during registry resolution
+- invalid ordering/state transitions in preprocessing chain
+- validation failure in `validate-output`
+- output write failure in `json` writer
+
+## Tests to inspect before changes
+
+- `internal/builtin/preprocess_test.go`
+- `internal/builtin/postprocess_test.go`
+- `internal/overlap/resolve_test.go`
+- `internal/overlap/detect_test.go`
+- `internal/coalesce/coalesce_test.go`
+- `internal/danglers/danglers_test.go`
+- `internal/backchannel/backchannel_test.go`
+- `internal/filler/filler_test.go`
+- `internal/autocorrect/autocorrect_test.go`
+- `internal/cli/merge_test.go`
+
+## Invariants
+
+- Modules are selected by canonical name through the registry.
+- Execution is sequential and deterministic for a fixed configuration.
+- `assign-ids` defines final public segment IDs.
+- `validate-output` enforces public artifact contracts through `schema`.
diff --git a/docs/internal/pipeline.md b/docs/internal/pipeline.md
new file mode 100644
index 0000000..386a063
--- /dev/null
+++ b/docs/internal/pipeline.md
@@ -0,0 +1,102 @@
+# Pipeline Internals
+
+## Purpose
+
+Describes implemented merge pipeline orchestration in `internal/pipeline`.
+
+## Inputs and outputs
+
+Input:
+
+- `config.Config`
+- registry-resolved modules from `internal/builtin`
+
+Output:
+
+- selected public artifact written by output writer modules
+- optional report JSON when `cfg.ReportFile` is set
+
+## Stage contracts
+
+The runner executes these contracts in order:
+
+1. `InputReader`: external inputs -> `[]model.RawTranscript`
+2. `Preprocessor`: `PreprocessState` transformations (`raw` -> `canonical`)
+3. `Merger`: canonical transcripts -> `model.MergedTranscript`
+4. `Postprocessor`: merged transcript transformations
+5. `OutputWriter`: serialized artifact writes
+
+`PreprocessState` must end in `StateCanonical` before merge.
+
+## Registry resolution
+
+`resolvePlan` maps configured names to modules:
+
+- input reader: `cfg.InputReader`
+- preprocessors: `cfg.PreprocessingModules`
+- postprocessors: `cfg.PostprocessingModules`
+- output writers: `cfg.OutputModules`
+- merger: single registered merger
+
+Unknown names fail fast with contextual errors.
+
+## Execution order and reporting
+
+- Modules run sequentially in configured order.
+- Events returned by modules are appended in execution order.
+- Report metadata includes input reader, input files, and module lists.
+- Output writer events are appended before optional report write.
+
+## Config fields used
+
+Runner-level fields:
+
+- `InputReader`
+- `InputFiles`
+- `PreprocessingModules`
+- `PostprocessingModules`
+- `OutputModules`
+- `OutputSchema` (via `artifact.SelectedFromMerged`)
+- `ReportFile`
+
+Module-specific settings are consumed inside builtin modules (for example
+coalesce gap and overlap thresholds).
+
+## Adapters used
+
+- Input adapters: registered `InputReader` implementations (default `json-files`).
+- Output adapters: registered `OutputWriter` implementations (default `json`).
+- Report adapter: `report.WriteJSON` when `cfg.ReportFile` is provided.
+
+## Boundaries
+
+- Pipeline does not parse CLI flags.
+- Pipeline does not normalize raw CLI strings.
+- Pipeline delegates conversion to public output contracts to `internal/artifact`.
+- Artifact-level commands `trim` and `normalize` are outside this pipeline.
+
+## Failure behavior
+
+Pipeline returns errors from:
+
+- registry resolution (unknown modules, missing merger)
+- invalid preprocessing state transitions
+- module read/process/merge/write failures
+- optional report write failure
+
+No retry/resume state is stored.
+
+## Tests to inspect before changes
+
+- `internal/pipeline/runner_test.go`
+- `internal/builtin/preprocess_test.go`
+- `internal/builtin/postprocess_test.go`
+- `internal/cli/merge_test.go`
+
+## Invariants
+
+- Sequential deterministic execution order.
+- Preprocessing state must type-check from `raw` to `canonical`.
+- Module selection is explicit by canonical names.
+- Report event order reflects actual execution order.
+- Output artifact selection is schema-driven via `internal/artifact`.
diff --git a/docs/policy/development.md b/docs/policy/development.md
new file mode 100644
index 0000000..6cef3ef
--- /dev/null
+++ b/docs/policy/development.md
@@ -0,0 +1,110 @@
+# Development Policy
+
+## Purpose
+
+This document defines contributor workflow for maintainers and coding agents.
+It complements [architecture policy](architecture.md) and
+[documentation policy](documentation.md).
+
+## Repository layout
+
+- `cmd/seriatim/`: process entrypoint.
+- `internal/cli/`: Cobra commands and flag wiring.
+- `internal/config/`: option normalization and validation.
+- `internal/pipeline/`: orchestration interfaces, registry, runner.
+- `internal/builtin/`: implemented input/pre/post/output modules and merger.
+- `internal/artifact/`: conversion from internal merged model to public shapes.
+- `internal/trim/`: artifact-level trim logic.
+- `internal/normalize/`: artifact-level normalize parsing/building.
+- `internal/*` domain packages: overlap, coalesce, danglers, filler,
+  backchannel, speaker, autocorrect, report, model.
+- `schema/`: public structs plus embedded JSON Schemas and validation.
+- `docs/`: policy, user docs, roadmap, and internal docs.
+
+## Local checks
+
+Primary repository check:
+
+```sh
+go test ./...
+```
+
+Useful manual checks for CLI-facing changes:
+
+```sh
+go run ./cmd/seriatim --help
+go run ./cmd/seriatim merge --help
+go run ./cmd/seriatim trim --help
+go run ./cmd/seriatim normalize --help
+```
+
+Current toolchain note:
+
+- There is no Makefile.
+- There is no taskfile.
+- There is no committed linter configuration.
+- There is no automated documentation checker.
+
+## Coding conventions
+
+- Keep core behavior deterministic for identical inputs/config/version.
+- Keep CLI command functions thin: parse flags, construct config, delegate.
+- Keep validation in `internal/config` and package-specific validators.
+- Return errors from deep logic; do not print inside internal packages.
+- Preserve clear package boundaries between adapters and domain transforms.
+
+## Dependency policy
+
+Prefer the Go standard library first.
+
+Third-party dependencies should stay narrow and justified. Current direct
+runtime dependencies are:
+
+- `github.com/spf13/cobra` for CLI structure.
+- `gopkg.in/yaml.v3` for YAML rule files.
+- `github.com/santhosh-tekuri/jsonschema/v6` for public schema validation.
+
+## Adding CLI flags
+
+1. Add the flag in the relevant `internal/cli/*.go` command.
+2. Thread the raw value through `config.*Options`.
+3. Add normalization/validation in `internal/config/config.go`.
+4. Update or add CLI/config tests.
+5. Update canonical docs (`docs/cli.md`, `docs/config.md`) if user-visible.
+
+## Adding config fields or environment variables
+
+1. Add field(s) to the relevant config struct(s).
+2. Parse and validate in `internal/config/config.go`.
+3. Add tests in `internal/config/config_test.go`.
+4. Thread validated values into consuming modules.
+5. Update `docs/config.md` and related docs.
+
+## Adding modules or pipeline behavior
+
+1. Implement the module in the appropriate package (often `internal/builtin`).
+2. Expose a stable module name via `Name()`.
+3. Register it in `internal/builtin/registry.go`.
+4. Ensure preprocessing modules declare correct `Requires()`/`Produces()`
+   states.
+5. Add/adjust tests in module packages and `internal/cli/merge_test.go`.
+6. Document internal behavior changes in `docs/internal/`.
+
+## Schema and artifact changes
+
+1. Update public structs and validation logic in `schema/`.
+2. Update embedded JSON Schema files (`schema/*.schema.json`) if contract
+   changes.
+3. Update conversion behavior in `internal/artifact`, `internal/trim`, and/or
+   `internal/normalize` as needed.
+4. Add tests in `schema/`, `internal/artifact/`, `internal/trim/`,
+   `internal/normalize/`, and CLI tests.
+5. Update user and internal docs that reference output contracts.
+
+## Documentation expectations
+
+- Outside `docs/roadmap/`, document only implemented behavior.
+- Keep canonical homes: CLI in `docs/cli.md`, config in `docs/config.md`,
+  operations in `docs/operations.md`, troubleshooting in
+  `docs/troubleshooting.md`, internals in `docs/internal/`.
+- When behavior changes, update docs in the same change.