"""The lint core, with no CLI attached.

Split out of `commands/lint.py` for the reason given in
`chemenu/search/service.py`: `run_lint()` is a pure function over a corpus
directory, and it was sitting in a module that imports `typer` and `rich`, so
no in-process caller could reach it without the CLI head.

Everything that decides *findings* lives here. Everything that decides *how a
terminal sees them* - the report file, the exit code, the flags - stays in
`commands/lint.py`. `render_markdown()` and `render_summary()` are on this side
of the line because the markdown report is a data product (it is what
`reports/` holds and what `kb/log.md` refers to), not terminal formatting.
"""
from __future__ import annotations

from datetime import date
from pathlib import Path

from collections import Counter

from chemenu import blocks, config, kb_collections, links
from chemenu.catalog import SHARD_THRESHOLD, group_pages
from chemenu.frontmatter_io import frontmatter_error
from chemenu.markdown_code import strip_code_spans
from chemenu.provenance import broken_raw_refs as find_broken_raw_refs
from chemenu.provenance import duplicate_raw_file_owners as find_duplicate_raw_file_owners
from chemenu.provenance import extract_inline_cites
from chemenu.provenance import legacy_citation_markers as find_legacy_citation_markers
from chemenu.provenance import legacy_source_pages as find_legacy_source_pages
from chemenu.provenance import orphan_footnote_defs as find_orphan_footnote_defs
from chemenu.provenance import uncovered_raw_files as find_uncovered_raw_files
from chemenu.provenance import undefined_footnote_refs as find_undefined_footnote_refs
from chemenu.page import Page
from chemenu.version import Version
from chemenu.kb_scan import (
    GENERATED_INDEX,
    WIKILINK_RE,
    build_link_graph,
    find_duplicate_title_paths,
    find_nested_pages,
    inbound_links,
    load_kb_pages,
)
from chemenu.type_resolver import resolver

# Style guide's one mechanically-checkable rule (hard oracle: a plain count).
# The rest of the style guide (tone, AI-phrase avoidance) is a soft/proxy judgment
# and stays with the LLM - see wiki-manage/wiki-ingest skill guidance, not lint.
#
# The unit is a quote, not a `>` line. It used to be the line, which measured
# the wrap width the rule has no opinion about: one quotation written long
# counted 1 and the same quotation wrapped at 100 columns counted 4. An author
# who took the finding seriously made the page harder to read to quiet it.


QUOTE_LIMIT = 2

# How many hub pages `most_linked` reports. Purely informational (wiki-status
# surfaces it); not a finding, so the cutoff only bounds report size.
MOST_LINKED_COUNT = 10


def count_quote_blocks(body: str) -> int:
    """How many distinct blockquotes `body` carries.

    A run of consecutive `>` lines is one quote; a blank line or any
    non-quoted line ends it. Code is masked out first, so a `>` inside a
    fenced shell transcript is a prompt, not a quotation.

    Lazy continuation - a quote whose wrapped lines drop the `>` - reads here
    as two quotes rather than one. That over-counts in the direction the limit
    already errs on, and the corpus prefixes every line, so the alternative
    (tracking paragraph state) buys nothing.
    """
    count, in_quote = 0, False
    for line in strip_code_spans(body).splitlines():
        is_quote = line.lstrip().startswith(">")
        if is_quote and not in_quote:
            count += 1
        in_quote = is_quote
    return count


def _display(path: Path) -> str:
    """A path for a report line: repo-root-relative if possible, the raw path
    otherwise (a fixture tree in a test, or any tree `config.ROOT` does not
    contain)."""
    try:
        return str(path.relative_to(config.ROOT))
    except ValueError:
        return str(path)


def find_misplaced(pages: dict[str, Page]) -> list[tuple[str, Page, Path]]:
    """(title, page, target_dir) for every page whose type resolves and whose
    current directory differs from the one `TypeResolver.compute_target_dir`
    would place it under - the same rule `new` places a page by. Shared by
    `misplaced_pages()` below and `wikitool move --reconcile`, which is the
    fix for what this finds.

    A page with no `type:` or an unresolvable one is skipped - each is
    reported separately, as `frontmatter_errors`/`type_resolution_errors`."""
    found = []
    for title, page in sorted(pages.items()):
        type_path = page.frontmatter.get("type")
        if not type_path:
            continue
        try:
            target_dir = resolver.compute_target_dir(type_path, page.frontmatter, page.path)
        except ValueError:
            continue
        if page.path.parent.resolve() != target_dir.resolve():
            found.append((title, page, target_dir))
    return found


def misplaced_pages(pages: dict[str, Page]) -> list[dict]:
    """Report form of `find_misplaced`: `{"page", "at", "should_be"}` per
    finding, for the lint report.

    Advisory rather than a hard error (see `HARD_ERROR_KEYS` below): plenty of
    existing instances predate `move`, and a hand-placed page is not a
    broken one - only one `wikitool move --page "<Title>"` would relocate."""
    return [
        {"page": title, "at": _display(page.path.parent), "should_be": _display(target_dir)}
        for title, page, target_dir in find_misplaced(pages)
    ]


def unclassified_source_pages(pages: dict[str, Page]) -> list[dict]:
    """Source pages sitting in the `unclassified` catalog slot.

    Advisory, like `misplaced_pages` above: `unclassified` is the visible
    fallback for a genuinely unclear source (Gitea #66, replacing the old
    silent `default: notes`), not a broken state - a page there is exactly as
    valid as one anywhere else, only waiting for someone to look at it and
    pick a real category with `wikitool touch --set source_type=<value>`."""
    return [
        {"page": title}
        for title, page in sorted(pages.items())
        if page.frontmatter.get("type") == "types/source.md"
        and page.frontmatter.get("source_type") == "unclassified"
    ]


def nested_pages(kb_dir: Path, pages: dict[str, Page]) -> list[dict]:
    """Report form of `find_nested_pages`: `{"page", "at", "depth"}` per
    finding.

    Hard rather than advisory, unlike `misplaced_pages` above: a hand-placed
    page in the wrong area is still a real page the catalog lists correctly.
    A page nested past an area is not - `group_pages` folds it into the area
    silently, so the *generated* catalog itself becomes wrong, which is the
    thing invariant 1 does not allow. There is also no version this becomes
    wrong at (unlike the migration-gated findings below): a nested page was
    always going to be misread by the catalog that reads it today."""
    return [
        {"page": title, "at": _display(page.path.parent), "depth": depth}
        for title, page, depth in find_nested_pages(kb_dir, pages)
    ]


def unsharded_collections(kb_dir: Path, pages: dict[str, Page]) -> list[dict]:
    """Collections past the catalog's shard threshold that have no areas to
    shard, together with the subtype split that would give them some.

    Sharding is already automatic, and it is per *area*: `index rebuild` hands
    an area over `SHARD_THRESHOLD` rows its own `INDEX.md`. Creating an area is
    not automatic and nothing ever asked for one - so a collection that never
    grew any keeps its whole catalog in a single table, past the threshold,
    forever. The threshold is then not a threshold but a dead value (Gitea
    #59), and this is the only check that can notice: an ingest sees one
    source and cannot see a collection's size, while `lint` sees the corpus and
    runs every 10 sources anyway.

    **A recommendation, not a failure** (it is deliberately absent from
    `HARD_ERROR_KEYS`), and narrow enough to stay one: it fires only where the
    split actually helps - every area it would create, the ungrouped remainder
    included, lands at or under the threshold. That self-limits in both
    directions. A collection under the threshold never fires, so a small
    `kb/comparisons/` is not permanently in the report; and a collection whose
    subtype values are lopsided (25 of 29 `source_type: notes`) does not fire
    either, because splitting it would produce one area over the threshold and
    a handful of splinters. What is left is a finding that appears when a
    collection grows into it and is silent when it does not.
    """
    findings: list[dict] = []
    for collection in group_pages(kb_dir, pages):
        if collection.count <= SHARD_THRESHOLD:
            continue
        # An area already exists, so the collection has been split once and
        # `index rebuild` shards whatever outgrows the threshold from here.
        # A page still sitting in the root is `misplaced_pages`' finding, not
        # this one.
        if any(area.name for area in collection.areas):
            continue

        counts: Counter[str] = Counter()
        fields: set[str] = set()
        # Whether every type writing here already declares the `layout:` that
        # turns the subtype into a directory. It decides which half of the fix
        # is still owed: without it there is nothing for `move` to compute a
        # destination from, with it the move is all that is left.
        layouts: set[bool] = set()
        for area in collection.areas:
            for page in area.pages:
                type_path = page.frontmatter.get("type")
                if not type_path:
                    continue
                try:
                    field = resolver.get_subtype_field(type_path, page.path)
                    layout = resolver.get_layout(type_path, page.path)
                except ValueError:
                    continue
                value = page.frontmatter.get(field) if field else None
                if not value:
                    continue
                counts[str(value)] += 1
                fields.add(str(field))
                layouts.add(bool(layout))

        if not counts:
            continue
        # The pages the subtype cannot place stay in the collection root, so
        # they are an area of their own for the purpose of this test.
        unplaced = collection.count - sum(counts.values())
        if max([*counts.values(), unplaced]) > SHARD_THRESHOLD:
            continue

        findings.append(
            {
                "collection": collection.name,
                "count": collection.count,
                "field": ", ".join(sorted(fields)),
                "layout_declared": layouts == {True},
                "distribution": [
                    {"value": value, "count": count}
                    for value, count in sorted(counts.items(), key=lambda kv: (-kv[1], kv[0]))
                ],
            }
        )
    return findings


def run_lint(kb_dir: Path) -> dict:
    pages = load_kb_pages(kb_dir)
    duplicate_titles = find_duplicate_title_paths(kb_dir, config.ROOT)

    # Pages whose frontmatter can't be parsed read back as `{}` everywhere
    # else, which would let them slip past every frontmatter-driven check
    # below with no finding at all - so they are detected explicitly.
    frontmatter_errors = []
    for title, page in sorted(pages.items()):
        reason = frontmatter_error(page.path)
        if reason is None and not page.frontmatter.get("type"):
            reason = "missing `type:` field"
        if reason is not None:
            frontmatter_errors.append({"page": title, "error": reason})

    graph = build_link_graph(pages)
    broken_links = [
        {"page": title, "target": target}
        for title, targets in graph.items()
        for target in sorted(targets)
        if target not in pages
    ]

    inbound = inbound_links({t: v for t, v in graph.items() if t != "index"})
    orphan_pages = sorted(
        title
        for title, sources in inbound.items()
        if not sources
        and title not in ("index", "log")
        # comparison pages are not linked to by design; index.md is sufficient coverage
        and pages[title].kind != "comparison"
    )

    # Same link graph, opposite end: the most-linked-to pages are the wiki's
    # hubs. Reported (not judged) so `wiki-status` can show them without
    # re-deriving the graph.
    inbound_counts = {title: len(sources) for title, sources in inbound.items()}
    most_linked = [
        {"page": title, "inbound": count}
        for title, count in sorted(inbound_counts.items(), key=lambda kv: (-kv[1], kv[0]))
        if count > 0
    ][:MOST_LINKED_COUNT]

    # The catalog is sharded: `kb/index.md` is a map carrying counts and links,
    # and the page rows live in a generated INDEX.md per collection/area. Both
    # halves have to be read, or every page reads as missing from the index.
    index_text = "".join(
        path.read_text(encoding="utf-8")
        for path in [kb_dir / "index.md", *sorted(kb_dir.rglob(GENERATED_INDEX))]
        if path.exists()
    )
    index_links = {m.group(1).strip() for m in WIKILINK_RE.finditer(index_text)}
    missing_from_index = sorted(set(pages) - index_links - {"index", "log"})
    dangling_index_entries = sorted(index_links - set(pages))

    title_mismatches = []
    for title, page in sorted(pages.items()):
        if page.kind not in ("entity", "concept"):
            continue
        h1 = page.h1_title
        if h1 is not None and h1 != title:
            title_mismatches.append({"page": title, "h1": h1})

    misplaced = misplaced_pages(pages)
    nested = nested_pages(kb_dir, pages)

    unmarked_provenance = []
    for title, page in sorted(pages.items()):
        if page.kind not in ("entity", "concept"):
            continue
        sources_list = page.frontmatter.get("sources") or []
        if not sources_list and page.frontmatter.get("provenance") != "general":
            unmarked_provenance.append(title)

    citation_frontmatter_drift = []
    for title, page in sorted(pages.items()):
        sources_list = set(page.frontmatter.get("sources") or [])
        cited = {cited_title for cited_title, _file in extract_inline_cites(page.body)}
        cited.discard(title)  # a source page citing itself for a specific file within it is not drift
        for missing_source in sorted(cited - sources_list):
            citation_frontmatter_drift.append({"page": title, "cited_but_not_in_sources": missing_source})

    legacy_citation_markers = find_legacy_citation_markers(pages)
    undefined_footnote_refs = find_undefined_footnote_refs(pages)
    orphan_footnote_defs = find_orphan_footnote_defs(pages)

    # The frontmatter half of the link graph. `broken_links` above only walks
    # `[[wikilinks]]` in page *bodies*, so a `related:`/`sources:`/`entities:`
    # entry naming a page that does not exist - a rename that was not
    # propagated, a deleted page, or a URL pasted where a title belongs - used
    # to pass every check. Which fields hold page titles is declared by each
    # type-spec's `page_ref_fields:`, not hardcoded here.
    # Resolved against the directory `run_lint()` was handed, not against
    # `config.KB_DIR`. A page under a tree that is not the configured corpus -
    # every fixture tree, and any `lint <path>` aimed elsewhere - raised
    # `ValueError` here and read as "no collection", which made the label
    # authorisation below skip the edge in silence rather than judge it
    # (Gitea #44).
    def _collection_of(page):
        try:
            return page.path.relative_to(kb_dir).parts[0]
        except (ValueError, IndexError):
            return None

    dangling_frontmatter_refs = []
    malformed_edges: list[dict] = []
    unlabelled_edges: list[dict] = []
    unauthorised_labels: list[dict] = []
    redundant_see_also: list[dict] = []

    # Every specific thing any page asserts about any pair, collected before the
    # loop below because the reverse direction of an edge is not known while
    # standing on the page that carries it.
    #
    # What it is for: `see-also` is the catalogue's declared last resort - it
    # asserts that nothing better fit. When the *other* page already says
    # something specific about the same pair (`Wine GE depends-on Wine` opposite
    # `Wine see-also Wine GE`), the weak edge adds nothing a reader did not
    # have: direction is authored but the inbound view is rendered, so the
    # labelled edge already shows on both pages. Measured once on this corpus,
    # that was 57 of 180 `see-also` edges - the largest single class, and none
    # of it a vocabulary gap.
    typed_edges: dict[tuple[str, str], str] = {}
    for source_title, source_page in pages.items():
        for edge in links.edges(source_page.frontmatter, "related"):
            if edge.is_labelled and edge.label != links.SEE_ALSO:
                typed_edges[(source_title, edge.target)] = edge.label

    for title, page in sorted(pages.items()):
        type_path = page.frontmatter.get("type")
        if not type_path:
            continue
        try:
            ref_fields = resolver.get_page_ref_fields(type_path, page.path)
        except ValueError:
            continue  # unresolvable type is already reported as type_resolution_errors
        for field in ref_fields:
            # Through `links` so a labelled edge (`- depends-on: Hermes`) is read
            # as its target rather than as a mapping - the entry carries the
            # label alongside the title now, and comparing the whole entry would
            # report every declared edge as dangling.
            for target in links.targets(page.frontmatter, field):
                if target not in pages:
                    dangling_frontmatter_refs.append(
                        {"page": title, "field": field, "target": target}
                    )
            for entry in links.malformed(page.frontmatter, field):
                malformed_edges.append(
                    {"page": title, "field": field, "entry": str(entry)}
                )
        # Labels are checked on `related:` only. `sources:`/`entities:`/
        # `concepts:` are the provenance path, unlabelled by construction.
        if "related" in ref_fields:
            source_collection = _collection_of(page)
            for edge in links.edges(page.frontmatter, "related"):
                if not edge.is_labelled:
                    unlabelled_edges.append({"page": title, "target": edge.target})
                    continue
                if edge.label == links.SEE_ALSO:
                    reverse_label = typed_edges.get((edge.target, title))
                    if reverse_label is not None:
                        redundant_see_also.append(
                            {
                                "page": title,
                                "target": edge.target,
                                "reverse_label": reverse_label,
                            }
                        )
                target_page = pages.get(edge.target)
                if source_collection is None or target_page is None:
                    continue
                destination = _collection_of(target_page)
                if destination is None:
                    continue
                allowed = kb_collections.authorised_labels(
                    source_collection, destination, kb_dir
                )
                if edge.label not in allowed:
                    unauthorised_labels.append(
                        {
                            "page": title,
                            "target": edge.target,
                            "label": edge.label,
                            "destination": destination,
                        }
                    )

    # A generated region whose markers do not pair up is not a tidiness problem:
    # the next write appends a second region beside it instead of replacing it,
    # and the page then carries two. An agent rewriting prose at the boundary is
    # how a marker goes missing, which is why this is a hard error.
    unbalanced_marker_findings = [
        {"page": title, "region": name}
        for title, page in sorted(pages.items())
        for name in blocks.unbalanced_markers(page.body)
    ]

    quote_limit_violations = []
    for title, page in sorted(pages.items()):
        quote_count = count_quote_blocks(page.body)
        if quote_count > QUOTE_LIMIT:
            quote_limit_violations.append({"page": title, "quote_count": quote_count})

    # Type system validation. Lint reports are not validated here: they are
    # written to `reports/` outside kb/ and are never pages, so nothing this
    # loop scans can be one.
    invalid_type_paths = []
    type_resolution_errors = []
    schema_validation_errors = []

    for title, page in sorted(pages.items()):
        type_path = page.frontmatter.get("type")
        if not type_path:
            continue

        # Check if type path is valid
        if not type_path.endswith('.md'):
            invalid_type_paths.append({"page": title, "type": type_path, "error": "Type path must end with .md"})
            continue

        # Try to resolve and validate the type
        try:
            resolver.load_type_spec(type_path, page.path)

            # Try schema validation
            try:
                resolver.validate_frontmatter(page.frontmatter, type_path, page.path)
            except ValueError as schema_error:
                schema_validation_errors.append({"page": title, "type": type_path, "error": str(schema_error)})

        except ValueError as resolution_error:
            type_resolution_errors.append({"page": title, "type": type_path, "error": str(resolution_error)})

    return {
        "generated": date.today().isoformat(),
        "page_count": len(pages),
        "frontmatter_errors": frontmatter_errors,
        "broken_links": broken_links,
        "orphan_pages": orphan_pages,
        "most_linked": most_linked,
        "inbound_counts": inbound_counts,
        "missing_from_index": missing_from_index,
        "dangling_index_entries": dangling_index_entries,
        "title_mismatches": title_mismatches,
        "duplicate_titles": duplicate_titles,
        "misplaced_pages": misplaced,
        "nested_pages": nested,
        "unsharded_collections": unsharded_collections(kb_dir, pages),
        "unclassified_source_pages": unclassified_source_pages(pages),
        "uncovered_raw_files": find_uncovered_raw_files(config.RAW_DIR, pages),
        "broken_raw_refs": find_broken_raw_refs(pages),
        "duplicate_raw_file_owners": find_duplicate_raw_file_owners(pages),
        "legacy_source_pages": find_legacy_source_pages(pages),
        "unmarked_provenance": unmarked_provenance,
        "citation_frontmatter_drift": citation_frontmatter_drift,
        "legacy_citation_markers": legacy_citation_markers,
        "undefined_footnote_refs": undefined_footnote_refs,
        "orphan_footnote_defs": orphan_footnote_defs,
        "dangling_frontmatter_refs": dangling_frontmatter_refs,
        "malformed_edges": malformed_edges,
        "unlabelled_edges": unlabelled_edges,
        "unauthorised_labels": unauthorised_labels,
        "redundant_see_also": redundant_see_also,
        "unbalanced_markers": unbalanced_marker_findings,
        "quote_limit_violations": quote_limit_violations,
        "invalid_type_paths": invalid_type_paths,
        "type_resolution_errors": type_resolution_errors,
        "schema_validation_errors": schema_validation_errors,
    }


def _section(lines: list[str], title: str, items: list, formatter) -> None:
    lines.append(f"## {title}")
    lines.append("")
    if not items:
        lines.append("None found.")
    else:
        for item in items:
            lines.append(f"- {formatter(item)}")
    lines.append("")


def render_markdown(report: dict) -> str:
    lines = [f"# Structural Lint Report ({report['generated']})", ""]
    lines.append(f"Scanned {report['page_count']} pages under `wiki/`. This report covers only")
    lines.append("mechanically-verifiable structural issues; see the Semantic Review section")
    lines.append("below for judgment calls the LLM should complete.")
    lines.append("")

    _section(
        lines, "Unreadable Frontmatter", report["frontmatter_errors"],
        lambda i: f"[[{i['page']}]] - {i['error']}",
    )
    _section(
        lines, "Broken Wikilinks", report["broken_links"],
        lambda i: f"[[{i['page']}]] links to missing [[{i['target']}]]",
    )
    _section(lines, "Orphan Pages (no inbound links)", report["orphan_pages"], lambda i: f"[[{i}]]")
    _section(
        lines, f"Most-Linked Pages (top {MOST_LINKED_COUNT} hubs)", report["most_linked"],
        lambda i: f"[[{i['page']}]] - {i['inbound']} inbound link(s)",
    )
    _section(lines, "Pages Missing from index.md", report["missing_from_index"], lambda i: f"[[{i}]]")
    _section(lines, "Dangling index.md Entries", report["dangling_index_entries"], lambda i: f"[[{i}]]")
    _section(
        lines, "Duplicate Titles (naming collisions)", report["duplicate_titles"],
        lambda i: f"`{i['stem']}` -> {', '.join(f'`{p}`' for p in i['paths'])}",
    )
    _section(
        lines, "Filename / H1 Title Mismatches", report["title_mismatches"],
        lambda i: f"[[{i['page']}]] H1 is '{i['h1']}'",
    )
    _section(
        lines, "Misplaced Pages (not under their type-spec's computed directory)",
        report.get("misplaced_pages", []),
        lambda i: f"[[{i['page']}]] is at `{i['at']}`, should be under `{i['should_be']}` "
        f"- `wikitool move --page \"{i['page']}\"`",
    )
    _section(
        lines, "Nested Pages (more than one directory below their collection)",
        report.get("nested_pages", []),
        lambda i: f"[[{i['page']}]] is {i['depth']} directories below `kb/` at `{i['at']}` - "
        "the catalog folds this into its area silently; `wikitool move --reconcile` fixes it "
        "when the page's type resolves to a shallower directory, otherwise move it up by hand",
    )
    _section(
        lines, f"Collections Past the Shard Threshold (>{SHARD_THRESHOLD}) With No Areas "
        "- recommendation, not an error",
        report.get("unsharded_collections", []),
        lambda i: f"`kb/{i['collection']}/` holds {i['count']} pages in a single table and has no "
        f"areas, so the per-area shard threshold never fires. Splitting on `{i['field']}` would "
        "give: "
        + ", ".join(f"{d['value']} {d['count']}" for d in i["distribution"])
        + f" - all at or under {SHARD_THRESHOLD}. "
        + (
            "The type-spec already declares the `layout:` for those values, so "
            "`wikitool move --reconcile` and `wikitool index rebuild` are the whole fix"
            if i.get("layout_declared")
            else "Declare a `layout:` for those values in the type-spec, then "
            "`wikitool move --reconcile` and `wikitool index rebuild`"
        ),
    )
    _section(
        lines, "Unclassified Source Pages (source_type: unclassified) - recommendation, not an error",
        report.get("unclassified_source_pages", []),
        lambda i: f"[[{i['page']}]] - `wikitool touch --set source_type=<value>` once its "
        "category is known",
    )
    _section(
        lines, "Uncovered Raw Files (no source page)", report["uncovered_raw_files"],
        lambda i: f"`{i}`",
    )
    _section(
        lines, "Broken raw_files References", report["broken_raw_refs"],
        lambda i: f"[[{i['page']}]] -> `{i['raw_path']}` (does not exist)",
    )
    _section(
        lines, "Raw Files With More Than One Owner", report["duplicate_raw_file_owners"],
        lambda i: f"`{i['raw_file']}` is claimed by " + ", ".join(f"[[{t}]]" for t in i["owners"]),
    )
    _section(
        lines, "Legacy source: Field (not yet migrated to raw_files:)", report["legacy_source_pages"],
        lambda i: f"[[{i['page']}]] source: `{i['source']}` ({i['reason']})",
    )
    _section(
        lines, "Pages Missing provenance: general Marker", report["unmarked_provenance"],
        lambda i: f"[[{i}]] has no sources and is not marked `provenance: general`",
    )
    _section(
        lines, "Citation / Frontmatter Drift", report["citation_frontmatter_drift"],
        lambda i: f"[[{i['page']}]] cites [[{i['cited_but_not_in_sources']}]] inline but it is missing from frontmatter `sources:`",
    )
    _section(
        lines, "Legacy Citation Markers (pre-migration `^[[...]]`)", report["legacy_citation_markers"],
        lambda i: f"[[{i['page']}]] still has `{i['marker']}` - run `wikitool cite add` and replace it with the `[^cite-id]` it prints",
    )
    _section(
        lines, "Undefined Footnote References", report["undefined_footnote_refs"],
        lambda i: f"[[{i['page']}]] references `[^{i['ref']}]`, which has no `[^{i['ref']}]: [[...]]` definition",
    )
    _section(
        lines, "Orphan Footnote Definitions", report["orphan_footnote_defs"],
        lambda i: f"[[{i['page']}]] defines `[^{i['id']}]` (-> [[{i['source']}]]) but nothing references it - run `wikitool cite sync`",
    )
    _section(
        lines, "Malformed Edges", report.get("malformed_edges", []),
        lambda i: f"[[{i['page']}]] `{i['field']}`: {i['entry']}",
    )
    _section(
        lines, "Unbalanced Generated-Region Markers", report.get("unbalanced_markers", []),
        lambda i: f"[[{i['page']}]]: `{i['region']}`",
    )
    _section(
        lines, "Unlabelled Edges", report.get("unlabelled_edges", []),
        lambda i: f"[[{i['page']}]] -> [[{i['target']}]]",
    )
    _section(
        lines, "Labels Not Authorised by the Source Collection",
        report.get("unauthorised_labels", []),
        lambda i: f"[[{i['page']}]] `{i['label']}` -> kb/{i['destination']}/ ([[{i['target']}]])",
    )
    _section(
        lines, "Redundant see-also (the other page already says something specific)",
        report.get("redundant_see_also", []),
        lambda i: f"[[{i['page']}]] `see-also` -> [[{i['target']}]], but [[{i['target']}]] already asserts `{i['reverse_label']}` back - drop the weaker edge, the inbound view renders the other one here",
    )
    _section(
        lines, "Dangling Frontmatter References", report["dangling_frontmatter_refs"],
        lambda i: f"[[{i['page']}]] `{i['field']}:` names `{i['target']}`, which is not a page",
    )
    _section(
        lines, "Invalid Type Paths", report["invalid_type_paths"],
        lambda i: f"[[{i['page']}]] has type: `{i['type']}` - {i['error']}",
    )
    _section(
        lines, "Type Resolution Errors", report["type_resolution_errors"],
        lambda i: f"[[{i['page']}]] type: `{i['type']}` - {i['error']}",
    )
    _section(
        lines, "Schema Validation Errors", report["schema_validation_errors"],
        lambda i: f"[[{i['page']}]] type: `{i['type']}` - {i['error']}",
    )
    _section(
        lines, f"Pages Exceeding Quote Limit (>{QUOTE_LIMIT}/page)", report["quote_limit_violations"],
        lambda i: f"[[{i['page']}]] has {i['quote_count']} quotes - trim or confirm they're load-bearing",
    )

    lines.append("## Semantic Review (LLM to complete)")
    lines.append("")
    lines.append("- Contradictions across pages: TODO")
    lines.append("- Stale claims (unconfirmed >6 months): TODO")
    lines.append("- Suggested new pages / missing cross-references: TODO")
    lines.append("")
    return "\n".join(lines)


# Sections that always carry content but are not findings, so the summary
# handles them separately: a hub list is a statistic, and the semantic review
# is the checklist that follows the report rather than part of it.
INFORMATIONAL_SECTIONS = ("Most-Linked Pages",)
SEMANTIC_REVIEW_SECTION = "Semantic Review"


def _split_sections(markdown: str) -> tuple[str, list[tuple[str, str]]]:
    """Cut a rendered report into its preamble and (title, body) sections."""
    preamble, *rest = markdown.split("\n## ")
    sections = []
    for part in rest:
        title, _, body = part.partition("\n")
        sections.append((title.strip(), body.strip()))
    return preamble.rstrip(), sections


def render_summary(report: dict) -> str:
    """The same report with the empty sections removed.

    On a healthy corpus the full report is better than 90% "None found.", so
    reading it in the terminal means paging past the answer. The file on disk
    stays complete - this is what gets printed, and the written path underneath
    it is how the rest is reached without running lint a second time.
    """
    preamble, sections = _split_sections(render_markdown(report))
    findings, trailing = [], []
    for title, body in sections:
        if title.startswith(SEMANTIC_REVIEW_SECTION):
            trailing.append((title, body))
        elif body != "None found." and not title.startswith(INFORMATIONAL_SECTIONS):
            findings.append((title, body))
    lines = [preamble, ""]
    if not findings:
        lines += ["No structural findings.", ""]
    for title, body in findings + trailing:
        lines += [f"## {title}", "", body, ""]
    return "\n".join(lines)


def default_report_path(report: dict) -> Path:
    """Where a report goes when the caller names no path.

    `reports/` is derived and gitignored ([reports/CONTRACT.md]), so writing
    here by default costs the tree nothing.
    """
    return config.ROOT / "reports" / f"Lint Report {report['generated']}.md"


# Findings that make a tree structurally wrong rather than merely untidy.
# `orphan_pages` is deliberately absent: many pages are validly reachable
# through the index or navigation only. `quote_limit_violations` is advisory
# too - it flags a habit, not a broken tree. `redundant_see_also` joins them for
# both of those reasons at once: a weak edge beside a specific one is redundant
# rather than wrong, and the check arrived long after the corpora it judges, so
# promoting it would turn every existing instance red on the upgrade that
# shipped it. Unlike `unlabelled_edges` it is not migration-gated either - there
# is no version at which the redundancy becomes an error, only a sweep someone
# does or does not get to.
#
# `misplaced_pages` is the same shape again: it arrived long after most
# instances' corpora were hand-placed, a hand-placed page is not a broken one,
# and there is no version at which "not under the computed directory" becomes
# wrong - only `wikitool move` someone does or does not get to run.
#
# `unsharded_collections` is advisory by construction rather than by tolerance:
# it does not describe anything that is wrong, only a collection that has grown
# past the size at which areas start paying for themselves. Whether to split it
# is an authoring decision about how the corpus is organised - the tool can see
# that the split would work and say so, and that is the whole of its authority.
# Failing on it would also make `lint` red on a corpus that is entirely
# self-consistent, which is the state the recommendation is asking to improve.
#
# `unclassified_source_pages` is advisory for the same reason `misplaced_pages`
# is: `unclassified` (Gitea #66) is a deliberately visible catalog slot for a
# source whose category is genuinely unclear, not a defect - failing on it
# would penalise the honest "I don't know yet" that the slot exists to allow,
# where the old silent `default: notes` hid the same uncertainty for free.
#
# `malformed_edges` and `unbalanced_markers` are hard from the start: neither
# describes an unconverted page, only a broken one.
#
# `nested_pages` is hard from the start too, and for the same reason as
# `malformed_edges`/`unbalanced_markers` rather than `misplaced_pages`'s: it is
# not a hand-placement habit some instances predate, it is a page the
# generated catalog (`index rebuild`) silently mis-describes today, on every
# instance, at every version - see `nested_pages()` above.
#
# One definition, used by `lint --fail-on-error` and by the eval scorecard: if
# the two disagreed, a run could pass its score while lint refused it.
HARD_ERROR_KEYS = (
    "frontmatter_errors",
    "broken_links",
    "dangling_index_entries",
    "duplicate_titles",
    "nested_pages",
    "broken_raw_refs",
    "duplicate_raw_file_owners",
    "legacy_source_pages",
    "citation_frontmatter_drift",
    "legacy_citation_markers",
    "undefined_footnote_refs",
    "orphan_footnote_defs",
    "dangling_frontmatter_refs",
    "malformed_edges",
    "unbalanced_markers",
    "unlabelled_edges",
    "unauthorised_labels",
    "invalid_type_paths",
    "type_resolution_errors",
    "schema_validation_errors",
)

# Findings that only become hard once the corpus has reached a given shape.
#
# `unlabelled_edges` and `unauthorised_labels` describe exactly the state a
# corpus is in between the 4.0.0 machinery landing and the migration reaching
# each page - the window `.wikitool-kb.json` exists to represent. Failing on
# them during that window would refuse the very corpus that
# `instructions/migrations/4.0.0-link-taxonomy.md` tells an instance to publish
# unit by unit. So the promotion is tied to `kb_version` rather than to a
# release date: below 4.0.0 they are advisory, at or above it an unlabelled
# edge is no longer a page awaiting conversion but an edge whose author did not
# say what it asserts.
#
# Gated rather than simply promoted, which is where this departs from
# `legacy_citation_markers`: that one was flipped in a later version and any
# instance still owing the citation migration had to live with a red lint. The
# ledger can answer the question now, so it does.
MIGRATION_GATED_KEYS: dict[str, Version] = {
    "unlabelled_edges": Version(4, 0, 0),
    "unauthorised_labels": Version(4, 0, 0),
}

_ALWAYS_HARD = Version(0, 0, 0)


def hard_error_keys(kb_version: Version | None = None) -> tuple[str, ...]:
    """`HARD_ERROR_KEYS` minus the findings this corpus has not grown into yet.

    `kb_version` defaults to what `.wikitool-kb.json` records. A tree without
    one - a fresh instance, which starts at the current shape rather than
    migrating into it - keeps every key: there is no outstanding migration for
    a gated finding to be the noise of.
    """
    from chemenu import kb_state

    if kb_version is None:
        kb_version = kb_state.read_kb_version()
    if kb_version is None:
        return HARD_ERROR_KEYS
    return tuple(
        key
        for key in HARD_ERROR_KEYS
        if kb_version >= MIGRATION_GATED_KEYS.get(key, _ALWAYS_HARD)
    )


def has_hard_errors(report: dict) -> bool:
    return any(report.get(key) for key in hard_error_keys())