fix: comparison and source pages accept the sources: cite add writes; sources may cite sources (#173)

Files changed:
- CHANGES.md
- VERSION
- instructions/wiki-ingest/SKILL.md
- kb/CONTRACT.md
- tools/CONTRACT.md
- tools/chemenu/commands/cite_cmd.py
- tools/chemenu/commands/xref.py
- tools/chemenu/tests/test_cite_cmd.py
- tools/chemenu/tests/test_page_ops.py
- tools/chemenu/tests/test_type_resolver.py
- tools/chemenu/tests/test_xref.py
- types/comparison.md
- types/comparison.schema.yaml
- types/source.md
- types/source.schema.yaml

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SnAJ7Z3CpVD3PRbN73QtU2

CHANGES.md

@@ -59,7 +59,7 @@ concern - readable here, never shipped as something to parse.
 
 ---
 
-## 8.0.0-beta.39 - 2026-10-04 - wiki-ingest and wiki-manage call xref add with --rel, not the --rel-a/--rel-b removed in 4.0.0
+## 8.0.0-beta.40 - 2026-10-04 - Comparison and source pages accept the sources: that cite add writes; sources may cite sources
 
 **Author:** Torben Nehmer
 
@@ -107,6 +107,7 @@ concern - readable here, never shipped as something to parse.
 - Link-Katalog: Beteiligungs- und RACI-Label von der Projektseite aus
 - Organisationsseiten: Personen als Abschnitt mit Aufstieg, entity_type organization, member-of, Lint-Befund broken_anchors
 - lint: Unfilled Template Sections - a section still holding only its template's TODO placeholders (advisory)
+- Comparison and source pages accept the sources: that cite add writes; sources may cite sources
 
 **Low impact**
 - version bump no longer points at version release in its output
@@ -152,6 +153,46 @@ concern - readable here, never shipped as something to parse.
 - wiki-ingest and wiki-manage call xref add with --rel, not the --rel-a/--rel-b removed in 4.0.0
 <!-- /wikitool:bumps -->
 
+### Comparison and source pages accept the sources: that cite add writes; sources may cite sources
+
+`cite add` writes the cited source into the page's `sources:`, but neither the `comparison` nor
+the `source` type declared that field, and both schemas set `additionalProperties: false`. So a
+comparison page cited the way `kb/comparisons/COLLECTION.md` asks for, or a source page citing one
+of its own raw files with `--file`, failed `lint` with `'sources' was unexpected`. Both types now
+declare `sources` as an optional array, in the schema and in `page_ref_fields:`. The second part
+matters: `rename`/`rm` carry only declared reference fields, and `lint` resolves only declared
+fields. A fix to the schema alone would leave dead `sources:` entries behind after a source is
+renamed, and nothing would report them.
+
+That also makes a citation between two sources legal: `cite add --page "Source - A" --source
+"Source - B"` records `Source - B` on A and leaves B alone. Two changes keep that edge directed:
+
+- `cite add` no longer writes a page's own title into its `sources:`. A source page citing its own
+  raw file gets the footnote definition and leaves `sources:` untouched, not even as an empty
+  list. `lint` and `citing_pages()` already ignored the self-edge.
+- `xref link-source` refuses a target that is itself a source page. It writes nothing for that
+  target, names it with the `cite add` command to use instead, links the others and exits 1. It
+  used to write `B.sources += A`, claiming the citation in the wrong direction, onto a page whose
+  schema then rejected it.
+
+`kb/CONTRACT.md` § Provenance and citation and `wiki-ingest` step 9 describe both.
+
+**What an existing instance has to do by hand.** The schema and type-spec of `comparison` and
+`source` belong to the instance once adopted. `dist upgrade` only renews the `.template` beside
+them, so the type half of this change does not arrive on its own. For each of the two types:
+
+1. Copy the `sources` property from `types/<type>.schema.yaml.template` into
+   `types/<type>.schema.yaml`.
+2. Add `sources` to `page_ref_fields:` in `types/<type>.md`. Without it a rename leaves the
+   entries pointing at the old title.
+3. Copy the `sources` row of the frontmatter table into the same file.
+
+An instance that has already loosened only the schema still needs step 2. The `cite add` and
+`link-source` changes are under `tools/` and arrive with the normal upgrade. Until the steps
+are done, `lint` keeps reporting a cited comparison or source page as a schema error, exactly as
+before. Nothing that worked before breaks. Found while writing the first comparison page of an
+instance on 7.0.0 (Gitea #173).
+
 ### wiki-ingest and wiki-manage call xref add with --rel, not the --rel-a/--rel-b removed in 4.0.0
 
 Since 4.0.0 `xref add` declares one directed edge and takes a single `--rel`, but the

VERSION

@@ -1 +1 @@
-8.0.0-beta.39
+8.0.0-beta.40

instructions/wiki-ingest/SKILL.md

@@ -351,6 +351,10 @@ validator complains - and the ticked list is the only record that they happened.
    call of its own, is `kb/CONTRACT.md` § Linking. The second links the new source to everything
    it backs in one pass.
 
+   An older source page the new one cites does not go into `--entities`: `link-source` refuses
+   it. Record it as a citation instead, `tools/wikitool cite add --page "Source - <Title>"
+   --source "<older source>"` - `kb/CONTRACT.md` § Provenance and citation has the rule.
+
 10. **Check coverage.**
 
     ```bash

kb/CONTRACT.md

@@ -300,7 +300,8 @@ Every claim is either traceable to a raw file or explicitly marked as not.
   [--file <qualifier>]` mints the id, upserts its `[[Source - X]]` (or
   `[[Source - X|storage-model.md]]` for a multi-file source) definition in the page's trailing
   Footnotes block (named per [Section headings](#section-headings)), and adds `Source - X` to
-  `sources:` - it prints the marker to paste at
+  `sources:` - unless the page *is* `Source - X`, citing one of its own raw files, since a page
+  never lists its own title there. It prints the marker to paste at
   the fact; placing it is still manual. Never hand-type a cite-id (AGENTS.md invariant 1). This
   differs from a plain `[[Source - X]]` link, which only means "related to".
 - **Notation inside code is notation, not a reference.** A `[^cite-id]` or a `[[wikilink]]`
@@ -309,13 +310,19 @@ Every claim is either traceable to a raw file or explicitly marked as not.
   means a marker appended to a line *inside* a fence cites nothing - put it on a source line
   under the block (`<source-word>: [^cite-id]`, in the KB language), where it renders as a
   footnote instead of travelling with the command when someone copies it.
-- A source cited inline must also appear in the page's frontmatter `sources:` list;
+- **A source page may cite another source page**, the same way any page does: `cite add --page
-  `wikitool lint` checks this in both directions, and hard-errors on a leftover pre-migration
+  "Source - A" --source "Source - B"` writes `Source - B` into A's `sources:` and leaves B
+  untouched. A citation between two sources has a direction, and `cite add` is the only command
+  that records it - `xref link-source` refuses a target that is itself a source page.
+- A source cited inline must also appear in the page's frontmatter `sources:` list - except a
+  source page's citation of itself, which never does; `wikitool lint` checks this in both
+  directions, and hard-errors on a leftover pre-migration
   `^[[...]]` marker, an undefined `[^cite-id]` reference, or an orphaned Footnotes definition.
   `tools/wikitool cite sync` reconciles a page's block after a prose edit changes which ids are
   actually referenced.
 - `tools/wikitool xref link-source --source "Source - X" --entities A,B,C` adds a new source
-  to every page it backs in one pass.
+  to every page it backs in one pass. Its targets are the pages the source *mentions*, never
+  another source page.
 - Every raw file is expected to be claimed by some source page;
   `tools/wikitool sources coverage` lists the ones that are not.
 

tools/CONTRACT.md

@@ -755,12 +755,14 @@ Batch-link a source page to every entity/concept it mentions.
 - 0    success
 - 1    Source page not found
 - 1    A page in `--entities` does not exist, or a target could not be written; the others were linked
+- 1    A page in `--entities` is itself a source page; the others were linked
 - 1    The source page itself could not be written after its targets were
 
 **ON FAILURE**
 
 - Source page not found -> Fix the title and retry once
 - A page in `--entities` does not exist, or a target could not be written; the others were linked -> Fix the named pages and re-run - safe, since every write is idempotent. `sources trace --page "<Title>"` shows who is already linked
+- A page in `--entities` is itself a source page; the others were linked -> Drop it from `--entities` and record the citation with `cite add --page "<citing source>" --source "<cited source>"` instead
 - The source page itself could not be written after its targets were -> Fix the write failure and re-run (idempotent)
 
 **NOTES**
@@ -769,6 +771,7 @@ Batch-link a source page to every entity/concept it mentions.
 - Which field a target lands in follows its collection (`kb/entities/` -> `entities:`), so a new collection needs no code change.
 - A target whose collection matches no reference field the source type declares is linked one way and named in the output.
 - A target that does not exist is skipped and named; the others are still linked, and the run then exits 1.
+- A target that is itself a source page is refused, named with the `cite add` command to use instead, and handled like a missing page: nothing is written for it, the others are still linked, and the run exits 1. `link-source` means "A mentions X" and writes `X.sources += A`, which for X = another source would claim the citation in the wrong direction; a citation between two sources has a direction only `cite add` records.
 - Idempotent in both directions. `--dry-run` reports what would be linked.
 
 **SEE ALSO**
@@ -897,7 +900,8 @@ Upsert a `[^cite-id]: [[Source - X]]` definition in a page's footnotes region.
 
 - Upserts a `[^cite-id]: [[Source - X]]` definition in the page's generated footnotes region, creating the region between `<!-- wikitool:footnotes -->` markers if absent.
 - Reuses the id when the page already cites this exact source/file pair, so a repeat changes nothing.
-- Adds `Source - X` to the page's frontmatter `sources:`.
+- Adds `Source - X` to the page's frontmatter `sources:` - except on `Source - X` itself: a source page citing one of its own raw files (`--file`) gets the definition and leaves `sources:` untouched, since a page never lists its own title there.
+- A source page may cite another source page this way - `cite add` is the command that records a citation between two sources, in the direction it was made.
 - Prints the `[^cite-id]` marker; pasting it into the prose is a manual, editorial step.
 - `--dry-run` reports without writing.
 

tools/chemenu/commands/cite_cmd.py

@@ -88,7 +88,12 @@ def upsert_citation(page: Page, source_title: str, qualifier: Optional[str]) ->
     """Ensure `page` has a Footnotes definition for (source_title, qualifier)
     and that source_title is in its frontmatter `sources:`. Returns
     (cite_id_to_use, new_body, changed) - reuses an existing definition for
-    the same pair instead of minting a duplicate id."""
+    the same pair instead of minting a duplicate id.
+
+    A source page citing itself (one of its own raw files, via `--file`) gets
+    the definition but no `sources:` entry - not even an empty list. An edge
+    to itself carries nothing, and `lint` and `provenance.citing_pages()`
+    already ignore it."""
     head, definitions = split_cite_block(page.body)
 
     existing_id = next(
@@ -103,10 +108,12 @@ def upsert_citation(page: Page, source_title: str, qualifier: Optional[str]) ->
         definitions[marker_id] = (source_title, qualifier)
         block_changed = True
 
-    sources = page.frontmatter.setdefault("sources", [])
+    sources_changed = False
-    sources_changed = source_title not in sources
+    if source_title != page.title:
-    if sources_changed:
+        sources = page.frontmatter.setdefault("sources", [])
-        sources.append(source_title)
+        sources_changed = source_title not in sources
+        if sources_changed:
+            sources.append(source_title)
 
     new_body = render_page_body(head, definitions)
     changed = block_changed or sources_changed or new_body != page.body
@@ -131,7 +138,11 @@ def upsert_citation(page: Page, source_title: str, qualifier: Optional[str]) ->
         "region, creating the region between `<!-- wikitool:footnotes -->` markers if absent.",
         "Reuses the id when the page already cites this exact source/file pair, so a repeat "
         "changes nothing.",
-        "Adds `Source - X` to the page's frontmatter `sources:`.",
+        "Adds `Source - X` to the page's frontmatter `sources:` - except on `Source - X` "
+        "itself: a source page citing one of its own raw files (`--file`) gets the definition "
+        "and leaves `sources:` untouched, since a page never lists its own title there.",
+        "A source page may cite another source page this way - `cite add` is the command that "
+        "records a citation between two sources, in the direction it was made.",
         "Prints the `[^cite-id]` marker; pasting it into the prose is a manual, editorial "
         "step.",
         "`--dry-run` reports without writing.",
@@ -168,7 +179,7 @@ def cite_add(
 ):
     """Upsert a Footnotes definition for `--source` (reusing it if the page
     already cites the same source/file pair) and ensure `--source` is in the
-    page's frontmatter `sources:`. Prints the `[^cite-id]` marker to paste
+    page's frontmatter `sources:` (unless the page is `--source` itself). Prints the `[^cite-id]` marker to paste
     into the prose - placing it is still the caller's job.
     """
     pages = load_kb_pages(config.KB_DIR)

tools/chemenu/commands/xref.py

@@ -389,6 +389,11 @@ def xref_remove(
         "linked one way and named in the output.",
         "A target that does not exist is skipped and named; the others are still linked, and "
         "the run then exits 1.",
+        "A target that is itself a source page is refused, named with the `cite add` command to "
+        "use instead, and handled like a missing page: nothing is written for it, the others "
+        "are still linked, and the run exits 1. `link-source` means \"A mentions X\" and writes "
+        "`X.sources += A`, which for X = another source would claim the citation in the wrong "
+        "direction; a citation between two sources has a direction only `cite add` records.",
         "Idempotent in both directions. `--dry-run` reports what would be linked.",
     ),
     failures=(
@@ -402,6 +407,11 @@ def xref_remove(
             reaction="Fix the named pages and re-run - safe, since every write is idempotent. "
             "`sources trace --page \"<Title>\"` shows who is already linked",
         ),
+        cli_contract.Failure(
+            cause="A page in `--entities` is itself a source page; the others were linked",
+            reaction="Drop it from `--entities` and record the citation with "
+            "`cite add --page \"<citing source>\" --source \"<cited source>\"` instead",
+        ),
         cli_contract.Failure(
             cause="The source page itself could not be written after its targets were",
             reaction="Fix the write failure and re-run (idempotent)",
@@ -431,6 +441,7 @@ def xref_link_source(
 
     linked: list[str] = []
     skipped: list[str] = []
+    refused: list[str] = []
     failed: list[str] = []
     unrouted: list[str] = []
     source_changed = False
@@ -439,6 +450,13 @@ def xref_link_source(
         if page is None:
             skipped.append(name)
             continue
+        if page.kind == "source":
+            # Refused rather than linked: this would write `name.sources +=
+            # source` ("name cites source" - the wrong direction), and the
+            # back-reference would add `source.sources += name` as well. Which
+            # of two sources cites the other is only said by `cite add`.
+            refused.append(name)
+            continue
         sources = page.frontmatter.setdefault("sources", [])
         if source not in sources:
             sources.append(source)
@@ -489,6 +507,12 @@ def xref_link_source(
         typer.echo(f"{verb} source '{source}' to: {', '.join(linked)}")
     if skipped:
         typer.echo(f"Skipped (page not found): {', '.join(skipped)}")
+    for name in refused:
+        typer.echo(
+            f"Refused (a source page - record a citation between sources with "
+            f"`wikitool cite add --page \"{source}\" --source \"{name}\"` if '{source}' cites it, "
+            f"or the other way round): {name}"
+        )
     if failed:
         typer.echo(f"Failed to write (fix and re-run for just these names): {', '.join(failed)}")
 
@@ -496,10 +520,12 @@ def xref_link_source(
         typer.echo("No files written (--dry-run).")
         return
 
-    if skipped or failed:
+    if skipped or refused or failed:
         parts = []
         if skipped:
             parts.append(f"page(s) not found: {', '.join(skipped)}")
+        if refused:
+            parts.append(f"source page(s) refused as targets: {', '.join(refused)}")
         if failed:
             parts.append(f"page(s) failed to write: {', '.join(failed)}")
         fail(f"Linked {len(linked)}/{len(names)} page(s); " + "; ".join(parts))

tools/chemenu/tests/test_cite_cmd.py

@@ -203,3 +203,121 @@ def test_cite_sync_command_over_kb(kb_dir, raw_dir, monkeypatch):
     result = runner.invoke(app, ["cite", "sync", "--all", "--dry-run"])
     assert result.exit_code == 0, result.output
     assert "No pages needed a Footnotes block change." in result.output
+
+
+# --- citing on comparison and source pages ----------------------------------
+#
+# Both types once declared no `sources:` field, while `cite add` wrote one onto
+# every page it touched - so a correctly cited comparison or source page failed
+# `lint` with `'sources' was unexpected`, under `additionalProperties: false`.
+
+
+def _write_source(kb_dir, title, raw_file):
+    """A source page the shipped schema accepts as it stands - the fixture's own
+    `Source - Aurora` carries a stray `source:` key and would mask the finding."""
+    from chemenu.frontmatter_io import write_page
+
+    path = kb_dir / "sources/notes" / f"{title}.md"
+    write_page(
+        path,
+        {
+            "type": "types/source.md", "source_type": "notes", "author": "Fixture Author",
+            "raw_files": [raw_file], "date": "2026-08-02", "summary": f"{title} summary",
+        },
+        f"\n# Source: {title}\n\n## Summary\n\nNotes.\n",
+    )
+    return path
+
+
+def _schema_errors_for(kb_dir, title):
+    from chemenu.lint_core import run_lint
+
+    return [e for e in run_lint(kb_dir)["schema_validation_errors"] if e["page"] == title]
+
+
+def test_cite_add_on_a_comparison_page_keeps_it_schema_valid(kb_dir, raw_dir):
+    from chemenu.cli import app
+    from chemenu.frontmatter_io import write_page
+
+    path = kb_dir / "comparisons/aurora vs Borealis.md"
+    write_page(
+        path,
+        {
+            "type": "types/comparison.md", "created": "2026-08-02",
+            "entities": ["aurora", "Borealis"], "summary": "Server against workstation",
+        },
+        "\n# Comparison: aurora vs Borealis\n\n## Überblick\n\nTwo machines.\n",
+    )
+    assert _schema_errors_for(kb_dir, "aurora vs Borealis") == []
+
+    result = runner.invoke(
+        app, ["cite", "add", "--page", "aurora vs Borealis", "--source", "Source - Aurora"]
+    )
+    assert result.exit_code == 0, result.output
+    fm, _body = read_page(path)
+    assert fm["sources"] == ["Source - Aurora"]
+    assert _schema_errors_for(kb_dir, "aurora vs Borealis") == []
+
+
+def test_a_source_page_may_cite_another_source_page(kb_dir, raw_dir):
+    """The citation lands on the citing side only, in the direction it was made."""
+    from chemenu.cli import app
+    from chemenu.provenance import citing_pages
+
+    path_a = _write_source(kb_dir, "Source - A", "raw/notes/Aurora.md")
+    path_b = _write_source(kb_dir, "Source - B", "raw/notes/Uningested.md")
+    before_b = path_b.read_bytes()
+
+    result = runner.invoke(app, ["cite", "add", "--page", "Source - A", "--source", "Source - B"])
+    assert result.exit_code == 0, result.output
+
+    fm_a, _body = read_page(path_a)
+    assert fm_a["sources"] == ["Source - B"]
+    assert path_b.read_bytes() == before_b
+    assert _schema_errors_for(kb_dir, "Source - A") == []
+    assert "Source - A" in citing_pages(load_kb_pages(kb_dir), "Source - B")
+
+
+def test_a_source_citing_its_own_file_writes_no_sources_entry(kb_dir, raw_dir):
+    """A self-citation names one of the page's own raw files. The definition is
+    written; `sources:` is left exactly as it was - not even an empty list."""
+    path = _write_source(kb_dir, "Source - A", "raw/notes/Aurora.md")
+    page = _reload(kb_dir, "Source - A")
+    assert "sources" not in page.frontmatter
+
+    marker_id, body, changed = upsert_citation(page, "Source - A", "Aurora.md")
+    assert changed is True
+    assert "sources" not in page.frontmatter
+    assert f"[^{marker_id}]: [[Source - A|Aurora.md]]" in body
+
+    page.body = body
+    _id, _body, changed_again = upsert_citation(page, "Source - A", "Aurora.md")
+    assert changed_again is False
+    assert path.exists()
+
+
+def test_a_self_citation_leaves_an_existing_sources_list_unchanged(kb_dir, raw_dir):
+    _write_source(kb_dir, "Source - A", "raw/notes/Aurora.md")
+    page = _reload(kb_dir, "Source - A")
+    page.frontmatter["sources"] = ["Source - Aurora"]
+
+    upsert_citation(page, "Source - A", "Aurora.md")
+    assert page.frontmatter["sources"] == ["Source - Aurora"]
+
+
+def test_cite_add_self_citation_on_disk(kb_dir, raw_dir):
+    from chemenu.cli import app
+
+    path = _write_source(kb_dir, "Source - A", "raw/notes/Aurora.md")
+    args = ["cite", "add", "--page", "Source - A", "--source", "Source - A", "--file", "Aurora.md"]
+    result = runner.invoke(app, args)
+    assert result.exit_code == 0, result.output
+
+    fm, body = read_page(path)
+    assert "sources" not in fm
+    assert f"[^{cite_id('Source - A', 'Aurora.md')}]: [[Source - A|Aurora.md]]" in body
+    assert _schema_errors_for(kb_dir, "Source - A") == []
+
+    again = runner.invoke(app, args)
+    assert again.exit_code == 0, again.output
+    assert "Already up to date" in again.output

tools/chemenu/tests/test_page_ops.py

@@ -193,6 +193,36 @@ def test_rename_fixes_a_dangling_source_reference(patched_wiki):
     assert frontmatter["sources"] == ["Source - Aurora Notes"]
 
 
+def test_rename_carries_sources_on_comparison_and_source_pages(patched_wiki):
+    """Both types declare `sources` in `page_ref_fields:`. A schema-only fix
+    would have let them validate, but a rename would then have left a dead
+    `sources:` entry behind on each - unreported, since `lint` resolves only
+    the declared fields too."""
+    from chemenu.lint_core import run_lint
+
+    write_page(
+        patched_wiki / "comparisons/aurora vs Borealis.md",
+        {"type": "types/comparison.md", "created": "2026-08-02",
+         "entities": ["aurora", "Borealis"], "sources": ["Source - Aurora"],
+         "summary": "Server against workstation"},
+        "\n# Comparison: aurora vs Borealis\n",
+    )
+    write_page(
+        patched_wiki / "sources/notes/Source - B.md",
+        {"type": "types/source.md", "source_type": "notes", "author": "Fixture Author",
+         "raw_files": ["raw/notes/Uningested.md"], "date": "2026-08-02",
+         "sources": ["Source - Aurora"], "summary": "B"},
+        "\n# Source: B\n",
+    )
+    page_ops.rename_command(old="Source - Aurora", new="Source - Aurora Notes", dry_run=False)
+
+    for path in ("comparisons/aurora vs Borealis.md", "sources/notes/Source - B.md"):
+        frontmatter, _body = read_page(patched_wiki / path)
+        assert frontmatter["sources"] == ["Source - Aurora Notes"]
+    dangling = {e["page"] for e in run_lint(patched_wiki)["dangling_frontmatter_refs"]}
+    assert not dangling & {"aurora vs Borealis", "Source - B"}
+
+
 def test_rename_stops_before_renaming_the_file_if_a_reference_write_fails(patched_wiki, monkeypatch):
     """A write failing partway through must not still rename the target file -
     that would leave some references pointing at the new title and others

tools/chemenu/tests/test_type_resolver.py

@@ -45,8 +45,8 @@ def test_get_page_ref_fields_reads_the_type_spec():
     so `lint`/`rename`/`rm` need no hardcoded list to update for a new type."""
     assert resolver.get_page_ref_fields("types/entity.md") == ["related", "sources"]
     assert resolver.get_page_ref_fields("types/concept.md") == ["related", "sources"]
-    assert resolver.get_page_ref_fields("types/source.md") == ["entities", "concepts"]
+    assert resolver.get_page_ref_fields("types/source.md") == ["entities", "concepts", "sources"]
-    assert resolver.get_page_ref_fields("types/comparison.md") == ["entities", "related"]
+    assert resolver.get_page_ref_fields("types/comparison.md") == ["entities", "related", "sources"]
 
 
 def test_page_ref_fields_exist_in_the_type_schema():

tools/chemenu/tests/test_xref.py

@@ -482,6 +482,38 @@ def test_xref_link_source_dry_run_leaves_the_source_page_alone(kb_dir):
     assert path.read_text(encoding="utf-8") == before
 
 
+def test_xref_link_source_refuses_a_target_that_is_itself_a_source(kb_dir):
+    """`link-source` means "A mentions X" and writes `X.sources += A`; for X =
+    another source that claims "B cites A", and the back-reference would add
+    `A.sources += B` too. A citation between sources has a direction, and only
+    `cite add` says which one - so the target is refused, the rest still linked."""
+    from chemenu.frontmatter_io import write_page
+
+    runner, app = _runner_env(kb_dir)
+    path_b = kb_dir / "sources/notes/Source - B.md"
+    write_page(
+        path_b,
+        {"type": "types/source.md", "source_type": "notes", "author": "Fixture Author",
+         "raw_files": ["raw/notes/Uningested.md"], "date": "2026-08-02", "summary": "B"},
+        "\n# Source: B\n",
+    )
+    result = runner.invoke(
+        app,
+        ["xref", "link-source", "--source", "Source - Aurora", "--entities", "gdeploy,Source - B"],
+    )
+    assert result.exit_code == 1
+    assert "Source - B" in result.output
+    assert 'cite add --page "Source - Aurora" --source "Source - B"' in result.output
+
+    pages = load_kb_pages(kb_dir)
+    assert "Source - Aurora" in pages["gdeploy"].frontmatter["sources"]
+    source_a = pages["Source - Aurora"].frontmatter
+    source_b = pages["Source - B"].frontmatter
+    for field in ("sources", "entities", "concepts"):
+        assert "Source - B" not in (source_a.get(field) or [])
+        assert "Source - Aurora" not in (source_b.get(field) or [])
+
+
 # --- the inbound view ------------------------------------------------------
 
 

types/comparison.md

@@ -4,7 +4,7 @@ name: comparison
 description: Structured type for comparison pages that set several entities or approaches against one another
 schema: types/comparison.schema.yaml
 base_dir: comparisons
-page_ref_fields: [entities, related]
+page_ref_fields: [entities, related, sources]
 guidance: types/comparison.guidance.md
 ---
 
@@ -24,6 +24,7 @@ and how to write a conforming page is [types/comparison.guidance.md](comparison.
 | `created` | Yes | Creation date (YYYY-MM-DD) |
 | `entities` | Yes | Titles of the entities compared |
 | `related` | No | Declared outbound edges - one `compares-with` edge per subject, written by `wikitool xref add` |
+| `sources` | No | Titles of the source pages cited on this page, written by `wikitool cite add` |
 | `summary` | Yes | One-liner for `kb/index.md` |
 
 ## Template

types/comparison.schema.yaml

@@ -38,6 +38,13 @@ properties:
       provenance-style list, so without this one the edge the page exists to
       make would live only in hand-written prose - which is the thing
       instructions/link-taxonomy.md was built to end.
+  sources:
+    type: array
+    items:
+      type: string
+    description: >-
+      Source page titles cited on this page, written by `wikitool cite add`.
+      Optional, so a comparison that cites nothing keeps validating without it.
   summary:
     type: string
     description: 1-line summary for index.md

types/source.md

@@ -6,7 +6,7 @@ schema: types/source.schema.yaml
 subtype_field: source_type
 base_dir: sources
 title_prefix: "Source - "
-page_ref_fields: [entities, concepts]
+page_ref_fields: [entities, concepts, sources]
 capture_fields: [fidelity, authority]
 guidance: types/source.guidance.md
 layout:
@@ -42,6 +42,7 @@ how to write a conforming page is [types/source.guidance.md](source.guidance.md)
 | `tags` | No | Navigation tags for categorization |
 | `entities` | No | Titles of the entities mentioned in this source |
 | `concepts` | No | Titles of the concepts mentioned in this source |
+| `sources` | No | Titles of *other* source pages this source cites, written by `wikitool cite add` - never its own title |
 | `summary` | Yes | One-liner for `kb/index.md` |
 
 ## Template

types/source.schema.yaml

@@ -72,6 +72,15 @@ properties:
     items:
       type: string
     description: Concept titles mentioned in this source
+  sources:
+    type: array
+    items:
+      type: string
+    description: >-
+      Other source pages this source cites, written by `wikitool cite add`.
+      Never this page's own title - a citation of one of its own raw files
+      leaves the field untouched. Optional, so a source that cites no other
+      source keeps validating without it.
   summary:
     type: string
     description: 1-line summary for index.md