sayd-core 0.1.0

//! Turn selected text into something worth hearing.
//!
//! Order matters: code fences are dropped before anything inspects their
//! contents, and whitespace is collapsed last so earlier removals do not
//! leave gaps.
//!
//! URLs get special handling. After code fences are dropped, the remaining
//! text is segmented into alternating runs of non-URL text and URL matches.
//! Transforms that must never touch URL text — hyphenation rejoin, markdown
//! stripping, acronym spelling — run only on the non-URL segments; the
//! `UrlPolicy` replacement (the literal word "link", a bare host, or the URL
//! verbatim) is computed only for the URL segments. The results are
//! concatenated back together in their original order.
//!
//! This replaces an earlier placeholder-based scheme (hide URLs behind
//! `\u{E000}<index>\u{E001}` markers, restore after the markdown/acronym
//! passes) that assumed those private-use codepoints never occur in real
//! input. That assumption doesn't hold: Nerd Font and Powerline glyphs live
//! in exactly that codepoint range, and this daemon's primary input is
//! terminal selections, so users routinely paste text containing them.
//! Segmentation makes no assumption about which codepoints appear anywhere
//! in the input — URL text and non-URL text are simply never in the same
//! string at the same time while the URL-unsafe transforms run.
//!
//! The two remaining passes — the control-character strip and whitespace
//! collapse — run once, globally, on the concatenated result, and that is
//! safe:
//!
//! - The control-character strip is unconditional and must stay that way:
//!   it is the only thing standing between an embedded NUL and a downstream
//!   FFI `CString::new` call, and a test pins that guarantee. Running it
//!   globally cannot corrupt a URL span because it only ever *removes*
//!   characters, and a legitimate URL cannot contain a control character in
//!   the first place — there is nothing there to protect.
//! - Whitespace collapse is safe to run globally because the `URL` regex's
//!   exclusion set already excludes whitespace from a URL match, so a URL
//!   span can never contain, start with, or end with whitespace. Collapsing
//!   whitespace runs elsewhere in the string can therefore never reach into
//!   a URL span or merge two URL spans together.
//!
//! Two of the transforms that *do* run per-segment inside `clean_non_url`
//! are anchor-based, and an anchor evaluated on an isolated segment does not
//! necessarily correspond to a real boundary in the original, unsegmented
//! input. Both are handled the same way: `clean_non_url` is given the real
//! character that precedes (and, for `ACRONYM`, follows) the segment in the
//! original input, and a sentinel is temporarily glued onto the segment edge
//! so the anchor sees what it would have seen unsegmented, then stripped
//! back off before the result is used.
//!
//! - `LIST_OR_HEADING` is anchored on `^` (line start, via `(?m)`). Handing
//!   it an isolated segment is wrong: position 0 of a segment that begins
//!   right after a URL is *not* a line start in the original text, but `^`
//!   would match there anyway (position 0 of *any* string it is handed is a
//!   line-start match, per `(?m)` semantics), misreading ordinary
//!   punctuation that follows a URL (` - `, ` # `, ` 1. `) as a
//!   bullet/heading/list marker. Position 0 of a segment is a genuine line
//!   start only when `prev` — the character immediately preceding the
//!   segment in the original input — is absent (segment starts at input
//!   position 0) or is a newline. When `prev` is anything else, a sentinel
//!   character is prepended before `LIST_OR_HEADING` runs, then stripped
//!   back off; `(?m)^` still correctly matches after any newline *inside*
//!   the segment, since the sentinel only occupies the position before the
//!   segment, not any position within it. The sentinel used is `'\u{1}'`
//!   (SOH, a C0 control character): it is not `\n`, so it never itself
//!   becomes a line start for `^` to match after; it is not whitespace, so
//!   `LIST_OR_HEADING`'s `\s*` cannot absorb it and then continue matching
//!   into the segment's real leading whitespace; and it is none of `#`,
//!   `-`, `*`, `+`, or a digit, so it can never itself begin a marker match.
//!   No other transform runs while it is present — it is pushed and popped
//!   within a single tightly-scoped step — so there is no window for it to
//!   be matched or mangled by `EMPHASIS`, `HYPHEN_BREAK`, or anything else.
//!   It also cannot leak into output even if some future bug skipped the
//!   strip-back-off step: the global, unconditional control-character
//!   filter at the end of `clean` removes every control character except
//!   `\n`/`\t`, and SOH is neither. A test
//!   (`bullet_immediately_followed_by_url_is_still_stripped`) confirms a
//!   marker is still stripped when a URL immediately follows it, and
//!   another (`marker_after_interior_newline_is_still_stripped`) confirms
//!   the sentinel does not suppress a legitimate match after a newline
//!   inside the segment.
//! - `ACRONYM` is anchored on `\b` (word boundary) at both ends. Evaluated
//!   on an isolated segment, `\b` at position 0 or at the end of the string
//!   is computed against "nothing" on the outside — even when the original
//!   input actually had an alphanumeric character right there (typically
//!   the edge of an adjacent URL), which would have suppressed the
//!   boundary. To reproduce full-string semantics, `clean_non_url` is given
//!   the real character that precedes and follows the segment in the
//!   original input; if that neighbor is alphanumeric, a one-character
//!   lowercase-letter sentinel is temporarily glued onto that side of the
//!   segment before `ACRONYM` runs (lowercase so it can never itself match
//!   `[A-Z]{3,}`), reproducing the same "word character on the other side"
//!   `\b` would have seen, and is stripped back off afterward.
//!
//! `LIST_OR_HEADING` and `HYPHEN_BREAK` both run inside `clean_non_url`, and
//! their relative order is load-bearing in the other direction: hyphenation
//! rejoin must run *first*. A hyphen-wrapped word can wrap onto a line that
//! is itself a marker line (`"machine-\n- learning"`), and `HYPHEN_BREAK`
//! needs to see the marker's leading `-` still in place to know there is a
//! non-word character between the two word halves and decline to touch
//! them; if the marker were stripped first, `HYPHEN_BREAK` would see
//! `"machine-\nlearning"` and rejoin it, silently fusing what was — genuinely
//! ambiguously, see the test below — either a wrapped hyphenated word or a
//! new list item.

use std::sync::LazyLock;

use regex::Regex;

use crate::config::{CleanupConfig, UrlPolicy};

static CODE_FENCE: LazyLock<Regex> =
    LazyLock::new(|| Regex::new(r"(?s)```.*?(?:```|$)").expect("static regex"));
// Excludes whitespace and the delimiters a URL is typically wrapped in
// (`<>()[]`), plus `*` and backtick, which are markdown emphasis/code
// syntax rather than realistic URL content. `_` and `-` are deliberately
// left in: both are common and legal in URLs (including hostnames).
static URL: LazyLock<Regex> =
    LazyLock::new(|| Regex::new(r"https?://[^\s<>\)\]*`]+").expect("static regex"));
static HYPHEN_BREAK: LazyLock<Regex> =
    LazyLock::new(|| Regex::new(r"(\w)-\s*\n\s*(\w)").expect("static regex"));
static EMPHASIS: LazyLock<Regex> =
    LazyLock::new(|| Regex::new(r"(\*\*|\*|__|_|`)").expect("static regex"));
static LIST_OR_HEADING: LazyLock<Regex> =
    LazyLock::new(|| Regex::new(r"(?m)^\s*(?:#{1,6}\s+|[-*+]\s+|\d+\.\s+)").expect("static regex"));
// Match only 3+ letter acronyms; two-letter words like OK and ID are left alone intentionally.
static ACRONYM: LazyLock<Regex> =
    LazyLock::new(|| Regex::new(r"\b[A-Z]{3,}\b").expect("static regex"));
static WHITESPACE: LazyLock<Regex> = LazyLock::new(|| Regex::new(r"\s+").expect("static regex"));

pub fn clean(text: &str, cfg: &CleanupConfig) -> String {
    let mut s = text.to_string();

    if cfg.drop_code_blocks {
        s = CODE_FENCE.replace_all(&s, " ").into_owned();
    }

    // Segment into alternating non-URL / URL runs so no transform below can
    // ever see both a URL and URL-unsafe syntax at once. See the module doc
    // comment for the full reasoning.
    let mut out = String::with_capacity(s.len());
    let mut last = 0;
    for m in URL.find_iter(&s) {
        let segment = &s[last..m.start()];
        let prev = s[..last].chars().next_back();
        let next = s[m.start()..].chars().next();
        out.push_str(&clean_non_url(segment, prev, next, cfg));
        out.push_str(&resolve_url(m.as_str(), cfg));
        last = m.end();
    }
    let segment = &s[last..];
    let prev = s[..last].chars().next_back();
    out.push_str(&clean_non_url(segment, prev, None, cfg));
    s = out;

    s = s
        .chars()
        .filter(|c| !c.is_control() || *c == '\n' || *c == '\t')
        .collect();

    if cfg.collapse_whitespace {
        s = WHITESPACE.replace_all(&s, " ").trim().to_string();
    }

    s
}

/// Apply the transforms that must never touch URL text to a non-URL segment.
///
/// `prev`/`next` are the characters that flank this segment in the
/// *original, unsegmented* input (e.g. the last character of a preceding
/// URL, or the first character of a following one) — `None` at the true
/// start/end of the input. They exist so `LIST_OR_HEADING`'s `^` and
/// `ACRONYM`'s `\b` anchors can be evaluated with full-string semantics; see
/// the module doc comment.
fn clean_non_url(
    segment: &str,
    prev: Option<char>,
    next: Option<char>,
    cfg: &CleanupConfig,
) -> String {
    let mut s = segment.to_string();

    if cfg.rejoin_hyphenation {
        s = HYPHEN_BREAK.replace_all(&s, "$1$2").into_owned();
    }

    if cfg.strip_markdown {
        s = strip_list_or_heading(&s, prev);
        s = EMPHASIS.replace_all(&s, "").into_owned();
        s = s.replace('|', " ");
    }

    if cfg.spell_acronyms {
        // `\b` at position 0 / end-of-string is computed against "nothing"
        // outside the segment, even when the real input had an alphanumeric
        // character right there. Reproduce that character with a lowercase
        // (never matched by `[A-Z]{3,}`) sentinel so the boundary check
        // sees what it would have seen unsegmented, then strip it back off.
        const SENTINEL: char = 'x';
        let prepend = prev.is_some_and(|c| c.is_alphanumeric());
        let append = next.is_some_and(|c| c.is_alphanumeric());

        let mut padded = String::with_capacity(s.len() + 2);
        if prepend {
            padded.push(SENTINEL);
        }
        padded.push_str(&s);
        if append {
            padded.push(SENTINEL);
        }

        let replaced = ACRONYM
            .replace_all(&padded, |caps: &regex::Captures| {
                caps[0]
                    .chars()
                    .map(|c| c.to_string())
                    .collect::<Vec<_>>()
                    .join(" ")
            })
            .into_owned();

        let start = if prepend { SENTINEL.len_utf8() } else { 0 };
        let end = replaced.len() - if append { SENTINEL.len_utf8() } else { 0 };
        s = replaced[start..end].to_string();
    }

    s
}

/// Strip markdown list/heading markers from `segment`, giving `(?m)^`
/// correct boundary knowledge about the *original, unsegmented* input.
///
/// Position 0 of `segment` is a genuine line start only when `prev` (the
/// character immediately preceding this segment in the original input) is
/// absent or is a newline; `(?m)^` cannot otherwise tell the difference
/// between that and a segment that merely begins wherever a URL was cut out
/// of the middle of a line. Whenever `prev` denotes anything else, a
/// sentinel is prepended before `LIST_OR_HEADING` runs and stripped back off
/// after. `(?m)^` still matches correctly after any newline *inside* the
/// segment regardless, since the sentinel only ever occupies the position
/// immediately before the segment's own text. See the module doc comment
/// for why `'\u{1}'` was chosen as the sentinel.
fn strip_list_or_heading(segment: &str, prev: Option<char>) -> String {
    const SENTINEL: char = '\u{1}';
    let needs_sentinel = !matches!(prev, None | Some('\n'));

    let padded = if needs_sentinel {
        let mut p = String::with_capacity(segment.len() + SENTINEL.len_utf8());
        p.push(SENTINEL);
        p.push_str(segment);
        p
    } else {
        segment.to_string()
    };

    let replaced = LIST_OR_HEADING.replace_all(&padded, "").into_owned();

    if needs_sentinel {
        // The sentinel can never itself be consumed by `LIST_OR_HEADING`
        // (see doc comment above), so it is always still there to strip.
        replaced.strip_prefix(SENTINEL).map(str::to_string).unwrap_or(replaced)
    } else {
        replaced
    }
}

/// Resolve a single matched URL span per `UrlPolicy`.
fn resolve_url(url: &str, cfg: &CleanupConfig) -> String {
    match cfg.urls {
        UrlPolicy::Link => "link".to_string(),
        UrlPolicy::Domain => host_of(url),
        UrlPolicy::Keep => url.to_string(),
    }
}

/// The host part of a URL, without scheme, port, path, query, fragment or
/// credentials.
///
/// Known-wrong, deferred: this splits the authority on `:` to strip the
/// port, which mangles IPv6 literals in brackets (e.g.
/// `https://[2001:db8::1]:8080/path`) because they contain colons of their
/// own. See `host_of_mangles_ipv6_literals_known_wrong_deferred` below for
/// the pinned baseline.
fn host_of(url: &str) -> String {
    let after_scheme = url.split("://").nth(1).unwrap_or(url);
    // The authority ends at the first path, query, or fragment delimiter.
    let authority_end = after_scheme
        .find(['/', '?', '#'])
        .unwrap_or(after_scheme.len());
    let authority = &after_scheme[..authority_end];
    authority
        .rsplit('@')
        .next()
        .unwrap_or(authority)
        .split(':')
        .next()
        .unwrap_or(authority)
        .to_string()
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::config::{CleanupConfig, UrlPolicy};

    fn all_on() -> CleanupConfig {
        CleanupConfig::default()
    }

    #[test]
    fn collapses_whitespace_runs() {
        let c = all_on();
        assert_eq!(clean("a   b\n\n\tc", &c), "a b c");
    }

    #[test]
    fn rejoins_hyphenated_line_breaks() {
        let c = all_on();
        assert_eq!(clean("inter-\nnational", &c), "international");
    }

    #[test]
    fn replaces_urls_with_the_word_link() {
        let c = all_on();
        assert_eq!(
            clean("see https://example.com/x?y=1 now", &c),
            "see link now"
        );
    }

    #[test]
    fn url_policy_domain_keeps_the_host() {
        let mut c = all_on();
        c.urls = UrlPolicy::Domain;
        assert_eq!(
            clean("see https://example.com/x now", &c),
            "see example.com now"
        );
    }

    #[test]
    fn url_policy_keep_leaves_it_alone() {
        let mut c = all_on();
        c.urls = UrlPolicy::Keep;
        assert_eq!(
            clean("see https://example.com now", &c),
            "see https://example.com now"
        );
    }

    #[test]
    fn strips_markdown_emphasis_and_code_ticks() {
        let c = all_on();
        assert_eq!(
            clean("**bold** and `code` and _em_", &c),
            "bold and code and em"
        );
    }

    #[test]
    fn strips_heading_hashes_and_list_bullets() {
        let c = all_on();
        assert_eq!(
            clean("# Title\n- one\n* two\n1. three", &c),
            "Title one two three"
        );
    }

    #[test]
    fn drops_fenced_code_blocks_entirely() {
        let c = all_on();
        let input = "before\n```rust\nfn main() {}\n```\nafter";
        assert_eq!(clean(input, &c), "before after");
    }

    #[test]
    fn unterminated_code_fence_drops_to_end_of_text() {
        let c = all_on();
        assert_eq!(clean("before\n```\nnever closed", &c), "before");
    }

    #[test]
    fn spells_out_allcaps_acronyms() {
        let c = all_on();
        assert_eq!(clean("the HTLC failed", &c), "the H T L C failed");
    }

    #[test]
    fn leaves_single_letters_and_normal_words_alone() {
        let c = all_on();
        assert_eq!(
            clean("I am OK with A and the DKG", &c),
            "I am OK with A and the D K G"
        );
    }

    #[test]
    fn strips_control_characters() {
        let c = all_on();
        assert_eq!(clean("a\u{0007}b\u{001b}c", &c), "abc");
    }

    #[test]
    fn every_transform_can_be_disabled() {
        let c = CleanupConfig {
            collapse_whitespace: false,
            rejoin_hyphenation: false,
            urls: UrlPolicy::Keep,
            strip_markdown: false,
            drop_code_blocks: false,
            spell_acronyms: false,
        };
        let input = "**x**  https://a.b\nHTLC";
        assert_eq!(clean(input, &c), input);
    }

    #[test]
    fn a_realistic_terminal_selection() {
        let c = all_on();
        let input = "error[E0308]: mismatched types\n  --> src/main.rs:12:5\n\nsee https://doc.rust-lang.org/E0308";
        let out = clean(input, &c);
        assert!(out.contains("mismatched types"));
        assert!(out.contains("link"));
        assert!(!out.contains('\n'));
    }

    #[test]
    fn empty_input_stays_empty() {
        assert_eq!(clean("", &all_on()), "");
    }

    #[test]
    fn strips_embedded_nul_bytes() {
        let c = all_on();
        assert_eq!(clean("before\u{0000}after", &c), "beforeafter");
    }

    #[test]
    fn url_policy_domain_strips_query_string_from_host() {
        let mut c = all_on();
        c.urls = UrlPolicy::Domain;
        assert_eq!(
            clean("go to https://example.com?x=1&y=2 now", &c),
            "go to example.com now"
        );
    }

    #[test]
    fn url_policy_domain_strips_fragment_from_host() {
        let mut c = all_on();
        c.urls = UrlPolicy::Domain;
        assert_eq!(
            clean("see https://example.com#section", &c),
            "see example.com"
        );
    }

    #[test]
    fn url_policy_domain_preserves_underscore_in_hostname() {
        let mut c = all_on();
        c.urls = UrlPolicy::Domain;
        assert_eq!(
            clean("see https://my_site.example.com/path now", &c),
            "see my_site.example.com now"
        );
    }

    #[test]
    fn url_policy_keep_preserves_underscore_when_stripping_markdown() {
        let mut c = all_on();
        c.urls = UrlPolicy::Keep;
        c.strip_markdown = true;
        assert_eq!(
            clean("see https://example.com/foo_bar/baz now", &c),
            "see https://example.com/foo_bar/baz now"
        );
    }

    #[test]
    fn url_policy_domain_strips_credentials_and_port() {
        let mut c = all_on();
        c.urls = UrlPolicy::Domain;
        assert_eq!(
            clean("see https://user:pass@example.com:8080/path now", &c),
            "see example.com now"
        );
    }

    // -- Placeholder-delimiter collision (Finding 1) -----------------------

    #[test]
    fn stray_placeholder_codepoints_alongside_a_real_url_are_not_swapped() {
        // The old scheme hid URLs behind `\u{E000}<index>\u{E001}` and
        // restored them with a whole-string `str::replace`. Input already
        // containing those exact codepoints collided with a real
        // placeholder of the same index and got silently overwritten with
        // unrelated URL text. With segmentation there is no placeholder to
        // collide with, so the stray codepoints must survive untouched and
        // the URL must resolve independently.
        let c = all_on();
        let out = clean("\u{E000}0\u{E001} see https://good.example.com/x now", &c);
        assert!(out.contains('\u{E000}') && out.contains('\u{E001}'));
        assert!(out.contains("link"));
        assert_ne!(out, "link see link now");
    }

    #[test]
    fn private_use_codepoints_with_no_url_pass_through_unmolested() {
        // Nerd Font / Powerline glyphs live in this exact private-use
        // range, and terminal selections are this daemon's primary input,
        // so these codepoints show up with no URL anywhere nearby. The old
        // scheme leaked raw, unresolved placeholder codepoints into speech
        // whenever the index didn't match a real URL; segmentation never
        // introduces a placeholder in the first place.
        let c = all_on();
        let input = "prompt \u{E0B0} branch \u{E000}\u{E001} done";
        assert_eq!(clean(input, &c), input);
    }

    // -- URL regex absorbing trailing markdown (Finding 2) ------------------

    #[test]
    fn url_policy_keep_strips_surrounding_markdown_emphasis() {
        let mut c = all_on();
        c.urls = UrlPolicy::Keep;
        c.strip_markdown = true;
        assert_eq!(
            clean("**https://example.com/a_b**", &c),
            "https://example.com/a_b"
        );
    }

    #[test]
    fn multiple_urls_domain_policy() {
        let mut c = all_on();
        c.urls = UrlPolicy::Domain;
        assert_eq!(
            clean(
                "see https://a.example.com/x and https://b.example.com/y now",
                &c
            ),
            "see a.example.com and b.example.com now"
        );
    }

    #[test]
    fn multiple_urls_keep_policy() {
        let mut c = all_on();
        c.urls = UrlPolicy::Keep;
        assert_eq!(
            clean(
                "see https://a.example.com/x and https://b.example.com/y now",
                &c
            ),
            "see https://a.example.com/x and https://b.example.com/y now"
        );
    }

    // -- Deferred: IPv6 literal baseline -------------------------------------

    #[test]
    fn host_of_mangles_ipv6_literals_known_wrong_deferred() {
        // `host_of` strips the port by splitting the authority on `:`,
        // which is wrong for a bracketed IPv6 literal: the literal's own
        // colons get split too, truncating the host to `[2001`. This
        // predates both fix rounds and is intentionally left as-is; this
        // test only pins the current (wrong) behaviour as a baseline for a
        // later fix.
        let mut c = all_on();
        c.urls = UrlPolicy::Domain;
        // The URL regex also stops at the literal's own `]` (excluded as a
        // URL-wrapping delimiter), so only `https://[2001:db8::1` is
        // matched as the URL; the rest becomes a trailing non-URL segment.
        assert_eq!(
            clean("see https://[2001:db8::1]:8080/path now", &c),
            "see [2001]:8080/path now"
        );
    }

    // -- Segment-boundary anchors (Finding 1: LIST_OR_HEADING's `^`) --------

    #[test]
    fn url_followed_by_punctuation_does_not_lose_its_separator() {
        // Regression: when LIST_OR_HEADING ran per non-URL segment, the
        // segment right after a URL started at position 0 of its own
        // string, which `^` (a line-start anchor) matched even though that
        // position is not a real line start in the original input. That
        // misread ordinary punctuation after a URL as a markdown marker and
        // silently ate it along with its whitespace, gluing words together.
        let c = all_on();
        assert_eq!(
            clean("see https://example.com/x - continued sentence", &c),
            "see link - continued sentence"
        );
        assert_eq!(
            clean("see https://example.com/x # not a heading", &c),
            "see link # not a heading"
        );
        assert_eq!(
            clean("call https://example.com/x 1. not a list", &c),
            "call link 1. not a list"
        );
    }

    #[test]
    fn bullet_immediately_followed_by_url_is_still_stripped() {
        // Confirms the reasoning in the module doc comment: LIST_OR_HEADING
        // now runs once over the whole input before segmentation, but a
        // marker that is genuinely at a line start — even one immediately
        // followed by a URL — must still be recognized and stripped. This
        // guards against over-correcting Finding 1 into never stripping
        // anything near a URL.
        let c = all_on();
        assert_eq!(clean("- https://example.com/x", &c), "link");
    }

    #[test]
    fn heading_and_numbered_list_still_stripped_alongside_a_url() {
        let c = all_on();
        let input = "# Title\n- see https://example.com/x\n1. done";
        assert_eq!(clean(input, &c), "Title see link done");
    }

    // -- Segment-boundary anchors (Finding 2: ACRONYM's `\b`) ----------------

    #[test]
    fn acronym_glued_directly_to_a_url_is_not_spelled_out() {
        // Regression: an acronym with no separating whitespace before a URL
        // has no real word boundary between them in the original text, so
        // it must not be spelled out. Both later designs (placeholder swap,
        // naive segmentation) regressed this by different mechanisms; the
        // round-1 implementation got it right because it ran ACRONYM once
        // over the whole string.
        let c = all_on();
        assert_eq!(clean("HTLChttps://example.com/x", &c), "HTLClink");
    }

    #[test]
    fn acronym_separated_from_a_url_by_whitespace_is_still_spelled_out() {
        // Guards against over-correcting Finding 2: the sentinel padding
        // must not suppress spelling out a legitimate acronym just because
        // a URL happens to follow later in the segment.
        let c = all_on();
        assert_eq!(clean("HTLC https://example.com/x", &c), "H T L C link");
    }

    #[test]
    fn url_at_very_start_and_very_end_of_input() {
        let c = all_on();
        assert_eq!(
            clean("https://example.com/a middle https://example.com/b", &c),
            "link middle link"
        );
    }

    // -- Fourth round: LIST_OR_HEADING restored to per-segment, sentinel-padded ^ --

    #[test]
    fn hyphen_wrap_onto_a_marker_line_does_not_fuse_the_two_words() {
        // "topics include machine-\n- learning models": whether this is a
        // hyphenated word wrapped across a line that happens to start with
        // "- learning", or a genuinely new list item reading "learning
        // models", is not decidable from the text alone — the source is
        // ambiguous. What matters is that HYPHEN_BREAK must not silently
        // fuse "machine" and "learning" into "machinelearning" with the
        // marker deleted out from under it (the bug this round fixes).
        // Restoring hyphenation-then-markers order means HYPHEN_BREAK sees
        // the marker character still in place and (for the non-digit
        // markers) declines to match, so the two halves stay separated once
        // the marker is later stripped.
        let c = all_on();
        assert_eq!(
            clean("topics include machine-\n- learning models", &c),
            "topics include machine- learning models"
        );
        assert_eq!(
            clean("topics include machine-\n# learning models", &c),
            "topics include machine- learning models"
        );
        assert_eq!(
            clean("topics include machine-\n* learning models", &c),
            "topics include machine- learning models"
        );
        // The numbered-list marker pins a different (also not-fused, but not
        // identical) outcome: `\d` is itself a `\w` character, so
        // HYPHEN_BREAK's own `(\w)` capture matches the leading digit of
        // "1." directly, rejoining across the newline before LIST_OR_HEADING
        // gets a chance to see a line-start "1." to strip. The digit ends up
        // glued to "machine" with the hyphen dropped, rather than a bullet
        // marker being stripped and a space surviving. This is pinned as
        // observed behavior, not endorsed as "correct" — the ambiguity
        // above applies here too, and `\d`-vs-`\w` overlap is a pre-existing
        // property of these two regexes, not something this round's fix
        // introduced or is scoped to change.
        assert_eq!(
            clean("topics include machine-\n1. learning models", &c),
            "topics include machine1. learning models"
        );
    }

    #[test]
    fn genuine_bullet_heading_and_numbered_list_are_still_stripped() {
        // Guards against under-correcting this round's fix: a real bullet
        // list, heading, and numbered list (no URL, no ambiguity) must still
        // be recognized and stripped exactly as before.
        let c = all_on();
        assert_eq!(clean("- one\n- two\n- three", &c), "one two three");
        assert_eq!(clean("# Heading text", &c), "Heading text");
        assert_eq!(clean("1. first\n2. second", &c), "first second");
    }

    #[test]
    fn marker_after_interior_newline_is_still_stripped() {
        // Proves the sentinel prepended at the *segment start* does not
        // suppress a legitimate `(?m)^` match after a newline further inside
        // the same segment — the sentinel only ever occupies the position
        // immediately before the segment, never a position within it.
        let c = all_on();
        assert_eq!(
            clean("intro line\n- bullet after newline", &c),
            "intro line bullet after newline"
        );
    }
}