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 | 162 | ✅     | sonnet | [Split the overloaded `meta` rule category](plan/162_rule-category-cleanup.md)                                            |
 | 163 | 🔲     |        | [Extract mdsmith Markdown parse/produce as a public Go library](plan/163_public-markdown-library.md)                      |
 | 164 | ✅     |        | [GitHub-UI-triggered releases and a split website deploy](plan/164_github-ui-releases-and-split-website.md)               |
+| 165 | 🔲     | opus   | [Portable Markdown export (mdsmith export)](plan/165_portable-markdown-export.md)                                         |
+| 166 | 🔲     | opus   | [Schema-driven data extraction (mdsmith extract)](plan/166_schema-driven-data-extraction.md)                              |
+| 167 | 🔲     | opus   | [Custom binding overrides for mdsmith extract](plan/167_custom-binding-overrides.md)                                      |
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@@ -0,0 +1,195 @@
+---
+id: 165
+title: Portable Markdown export (mdsmith export)
+status: "🔲"
+model: opus
+depends-on: []
+summary: >-
+  Add an `export` subcommand that writes a portable,
+  directive-free copy of a Markdown file: markers
+  removed, generated bodies kept, includes inlined.
+---
+# Portable Markdown export (mdsmith export)
+
+## Goal
+
+`mdsmith export <file>` writes a portable copy of a
+Markdown file with every `<?…?>` directive marker
+removed. Generated bodies stay as plain Markdown and
+`<?include?>` content is inlined. The result renders
+identically on any Markdown tool with no mdsmith
+knowledge.
+
+## Why a separate command
+
+This is not schema extraction. `extract` (plan 166)
+projects a kind's schema into a data tree. `export` is a
+source-to-source transform of the document itself. It
+needs no kind, schema, or conformance gate — only that
+the file parses and its directive bodies are fresh.
+
+Mixing it into `extract --format markdown` would couple a
+plain-document transform onto the schema-projection
+command. A dedicated `export` keeps the two concerns
+apart and leaves room to grow (output path, later batch).
+
+## Staleness: check by default, never auto-fix
+
+`export` does **not** silently regenerate directive
+bodies. Auto-fixing on export is surprising and would
+mask drift between a directive and its rendered body.
+The default is to *check*, not to *fix*:
+
+- **Default (check).** Before stripping, verify each
+  directive body equals what the engine would generate.
+  If any body is stale, export writes nothing and exits
+  non-zero with a diagnostic naming the stale directive
+  and advising `mdsmith fix` or `--fix`. The export is
+  faithful — it never papers over drift.
+- **`--no-check`.** Skip the staleness check and export
+  bodies exactly as they appear in the file. For callers
+  who know the file is fresh or deliberately want the
+  on-disk bytes.
+- **`--fix`.** Regenerate stale bodies in memory (same
+  engine as `mdsmith fix`) before stripping. Opt-in
+  convenience for a one-shot fresh export.
+
+`--fix` and `--no-check` are mutually exclusive (one
+regenerates, the other trusts as-is); passing both is a
+usage error. In every mode the source file is never
+modified.
+
+## Behavior
+
+- Drop the opening and closing marker lines of every
+  directive region; keep the body text between them
+  verbatim (regenerated first only under `--fix`).
+- `<?include?>` bodies are already expanded by
+  regeneration, so keeping the body inlines the included
+  content (recursively).
+- Markerless directives with no body (for example
+  `<?allow-empty-section?>`, `<?require?>`) are removed
+  outright.
+- Only lines the engine's marker-pair detection
+  recognizes as real directive start/end markers are
+  removed. Marker-like text the engine treats as literal
+  content (for example inner same-type markers nested in
+  an outer directive) is left untouched.
+- After stripping, normalize blank lines so the output is
+  stable and lint-clean. Front matter is kept as-is.
+- Exporting an already directive-free file is a no-op;
+  `export` is idempotent.
+
+## Tasks
+
+1. **Export core (red/green).** Add `internal/export`
+   with `Export(f *lint.File, mode Mode) ([]byte,
+   []lint.Diagnostic)` — mirroring plan 166's `Extract`
+   signature. It operates purely on the already-parsed
+   in-memory `*lint.File`, so it performs no I/O and
+   returns no `error`; file reads and `-o` writes are the
+   CLI layer's job (task 5) and surface as a real `error`
+   there. Contract: exactly one of the two return values
+   is populated. **Success** → the exported bytes (which
+   are never `nil`, since a directive-free file still
+   yields its own content) and a `nil` diagnostic slice.
+   **Refusal** (stale body in `Check` mode, or any
+   document-level problem) → `nil` bytes and a non-empty
+   diagnostic slice; the caller exits non-zero. `Mode` is
+   the staleness mode from task 4. Unit-test marker
+   removal, body retention, include-body inlining, and
+   the no-directive no-op.
+2. **Nested / literal-content markers.** Drive removal
+   off the engine's own marker-pair detection —
+   `gensection.FindMarkerPairs` in
+   [internal/archetype/gensection](../internal/archetype/gensection/parse.go),
+   whose `MarkerPair.StartLine`/`EndLine` give the exact
+   start- and end-marker line for every directive (not
+   just the include/catalog *body* ranges that
+   `lint.File.GeneratedRanges` records for diagnostic
+   suppression). Only lines the engine recognizes as real
+   markers are removed, so inner same-type markers that
+   the engine treats as literal content survive. Add a
+   test.
+3. **Whitespace normalization.** Collapse the blank
+   lines left by removed markers so output is stable and
+   passes `mdsmith check`. Test idempotence: export of
+   export equals export.
+4. **Staleness check and modes.** Add a checker that
+   compares each directive's on-disk body to what the
+   engine would generate, reusing the `mdsmith fix`
+   directive engine. `Mode` is `Check` (default), `Fix`,
+   or `NoCheck`. In `Check`, each stale body appends one
+   `lint.Diagnostic` (naming the directive, positioned at
+   its start marker) and `Export` returns `nil` bytes.
+   `Fix` regenerates stale bodies in memory before
+   stripping. `NoCheck` skips the comparison. The CLI
+   maps `--fix`/`--no-check` to the mode and rejects the
+   combination. Unit-test all three modes on a stale
+   fixture.
+5. **`export` subcommand.** Register `export` in
+   [main.go](../cmd/mdsmith/main.go); `mdsmith export
+   <file>` writes to stdout, `-o/--output <path>` writes
+   a file, `--fix` and `--no-check` select the staleness
+   mode (rejecting the combination). Never mutate the
+   source. Reuse the config and file-load helpers that
+   back `fix` in [main.go](../cmd/mdsmith/main.go). Exit
+   non-zero with a clear message on parse errors and on a
+   stale body in the default mode.
+6. **Fixtures and integration test.** Add `testdata`
+   inputs covering include, catalog, toc, and build
+   directives with golden directive-free outputs. Add a
+   stale-body fixture: assert default mode exits non-zero
+   with no output, `--fix` produces the fresh golden, and
+   `--no-check` exports the stale bytes as-is. Assert
+   idempotence and that fresh output passes `mdsmith
+   check`.
+7. **Docs.** Add `docs/reference/cli/export.md` (covering
+   the default check, `--fix`, and `--no-check`) and link
+   it from the CLI reference catalog. Run `mdsmith fix`
+   so catalogs and PLAN.md regenerate.
+
+## Acceptance Criteria
+
+- [ ] `mdsmith export <file>` removes every line the
+      engine recognizes as a real directive start/end
+      marker, keeps generated bodies, and inlines
+      `<?include?>` content. Marker-like text treated as
+      literal content is left in place.
+- [ ] The source file is never modified in any mode.
+- [ ] Default mode: a stale directive body makes
+      `export` exit non-zero with a diagnostic naming the
+      directive and writes no output.
+- [ ] `--fix` regenerates stale bodies in memory before
+      stripping; `--no-check` exports on-disk bytes as-is;
+      passing both is a usage error.
+- [ ] Nested same-type literal-content markers are
+      preserved.
+- [ ] Output is idempotent and (when fresh) passes
+      `mdsmith check`.
+- [ ] `-o <path>` writes to a file; stdout is the
+      default.
+- [ ] A parse error or missing file exits non-zero with
+      a clear message.
+- [ ] All tests pass: `go test ./...`
+- [ ] `go tool golangci-lint run` reports no issues
+- [ ] `mdsmith check .` passes
+
+## Decisions
+
+- **Keep generated bodies.** Markers are stripped but
+  TOC, catalog, and included content stay as plain
+  Markdown; includes are inlined for a portable copy.
+- **New `export` subcommand.** Not a fourth `extract`
+  format and not a `fix` flag; a dedicated command keeps
+  the source-to-source transform separate from schema
+  extraction.
+- **Check by default, never auto-fix.** A stale body
+  fails the export rather than being silently
+  regenerated, so the output faithfully reflects the
+  file. `--fix` opts into regeneration; `--no-check`
+  opts out of the check.
+- **Front matter retained.** It is not a directive;
+  stripping it is out of scope.
+- **Single file first.** Directory or glob batch export
+  is a possible follow-up, not in this plan.