feat(papers): find papers on arXiv, shelve the PDF, catalogue the note

Corrects a misread of the design. I had built this as "read the vault to
find papers"; the vault is the CARD CATALOGUE, not the source. Papers are
found on arXiv, the PDF is pulled down and shelved in our own library,
and a note recording it goes in the vault.

Three parts, and which is which matters:
  arXiv       — where papers are found
  blob store  — the shelf; the PDF lives there (cm-files, local + S3)
  the vault   — the catalogue; one note per paper, pointing at the shelf

The checkmark list (corpus, 0064) is what makes this continuous rather
than a job that redoes itself every week — the failure that killed the
previous attempt (0030-0044, dropped in 0053).

The load-bearing detail: every catalogue note carries
`source_id: arxiv:NNNN.NNNNN` in frontmatter, which is exactly the key
corpus::parse_note reads. So the checkmark list is rebuildable FROM the
vault. If the database were lost, re-indexing restores what we have —
the catalogue is authoritative, the index is derived. A test asserts that
round trip rather than trusting the two halves to agree.

Version suffixes are stripped (2401.12345v3 -> 2401.12345) or a weekly
job re-downloads a paper every time authors post a revision. Fetches are
rejected unless the bytes start with %PDF: arXiv serves an HTML holding
page while a PDF renders, and shelving that leaves a file that looks
present and is unreadable.

Verified against live arXiv, not fixtures:
  arxiv:2607.29678 TokTier: Exact Stateful Tokenization for Agentic LLM…
  arxiv:2607.29677 ExtractBench: A Benchmark for Schema-Guided Enterpri…
  arxiv:2607.29658 Reusing Past Repairs Through Hierarchical Trajectory…
  pdf: 1,361,770 bytes, %PDF verified

388 tests, clippy clean.

Co-Authored-By: Claude Opus 5 <[email protected]>

crates/cm-api/src/lib.rs

@@ -18,6 +18,7 @@ pub mod mission_orchestrator;
 pub mod mission_refiner;
 pub mod corpus;
 pub mod mission_delivery;
+pub mod papers;
 pub mod phase_config;
 pub mod runtime_preflight;
 pub mod mission_runtime;

crates/cm-api/src/papers.rs

@@ -0,0 +1,345 @@
+//! Finding papers, shelving them, and cataloguing them.
+//!
+//! The library has three parts and it matters which is which:
+//!
+//! - **arXiv** is where papers are *found*.
+//! - **The blob store** is the *shelf* — the PDF itself lives there.
+//! - **The vault** is the *card catalogue* — a markdown note per paper, with
+//!   the metadata and a pointer to the shelf.
+//!
+//! Plus [`crate::corpus`], which is the list of checkmarks: it is what stops
+//! the same paper being fetched twice across weekly runs. That list is the
+//! reason this can be a *continuous* job rather than one that redoes itself
+//! forever — the failure that killed the previous attempt at this (migrations
+//! 0030-0044, dropped in 0053).
+//!
+//! # The contract that ties it together
+//!
+//! Every note this module writes carries `source_id: arxiv:NNNN.NNNNN` in its
+//! frontmatter. `corpus::parse_note` reads exactly that key, so re-indexing
+//! the vault re-derives the checkmark list from the notes themselves. The
+//! catalogue is authoritative; the index is rebuildable from it. If the
+//! database were lost, a re-index of the vault would restore what we have.
+
+use serde::{Deserialize, Serialize};
+
+/// One paper as arXiv describes it.
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+pub struct Paper {
+    /// Bare arXiv id, e.g. `2401.12345` — no version suffix.
+    pub arxiv_id: String,
+    pub title: String,
+    pub authors: Vec<String>,
+    pub summary: String,
+    pub published: String,
+    pub pdf_url: String,
+}
+
+impl Paper {
+    /// The checkmark key. Version suffixes are stripped upstream so `v1` and
+    /// `v2` of the same paper are one entry, not two.
+    pub fn source_id(&self) -> String {
+        format!("arxiv:{}", self.arxiv_id)
+    }
+
+    /// Where the PDF is shelved in the blob store.
+    pub fn blob_key(&self) -> String {
+        format!("papers/arxiv/{}.pdf", self.arxiv_id)
+    }
+
+    /// Where the catalogue note goes in the vault.
+    ///
+    /// Under a dedicated folder so the library never collides with the
+    /// hand-written parts of the vault (`30 Resources`, `40 Projects`, and so
+    /// on). A human should always be able to tell which notes a machine wrote.
+    pub fn note_path(&self) -> String {
+        format!("60 Papers/arxiv-{}.md", self.arxiv_id)
+    }
+}
+
+/// Strip an arXiv version suffix: `2401.12345v3` -> `2401.12345`.
+///
+/// Without this a weekly job re-downloads a paper every time the authors post
+/// a revision, and the checkmark list quietly fills with near-duplicates.
+pub fn normalize_arxiv_id(raw: &str) -> String {
+    let id = raw.rsplit('/').next().unwrap_or(raw);
+    match id.find('v') {
+        // Only a trailing `vN` counts; the `v` in a word must not truncate.
+        Some(i) if id[i + 1..].chars().all(|c| c.is_ascii_digit()) && i + 1 < id.len() => {
+            id[..i].to_string()
+        }
+        _ => id.to_string(),
+    }
+}
+
+/// Parse arXiv's Atom feed.
+///
+/// Hand-rolled rather than pulling an XML crate: the feed is a fixed, simple
+/// shape and this reads five fields from it. If arXiv's format ever drifts,
+/// `entries_are_parsed_from_a_real_feed` fails loudly rather than silently
+/// returning zero papers — which is the failure mode that matters, because a
+/// search returning nothing looks exactly like "no new papers this week".
+pub fn parse_atom(xml: &str) -> Vec<Paper> {
+    let mut out = Vec::new();
+    for chunk in xml.split("<entry>").skip(1) {
+        let entry = chunk.split("</entry>").next().unwrap_or(chunk);
+        let field = |tag: &str| -> Option<String> {
+            let open = format!("<{tag}>");
+            let close = format!("</{tag}>");
+            let start = entry.find(&open)? + open.len();
+            let end = entry[start..].find(&close)? + start;
+            Some(unescape(entry[start..end].trim()))
+        };
+
+        let Some(raw_id) = field("id") else { continue };
+        let arxiv_id = normalize_arxiv_id(&raw_id);
+        if arxiv_id.is_empty() {
+            continue;
+        }
+        let Some(title) = field("title") else { continue };
+
+        let authors = entry
+            .split("<author>")
+            .skip(1)
+            .filter_map(|a| {
+                let start = a.find("<name>")? + 6;
+                let end = a[start..].find("</name>")? + start;
+                Some(unescape(a[start..end].trim()))
+            })
+            .collect();
+
+        // The PDF link is an attribute, not an element.
+        let pdf_url = entry
+            .split("<link")
+            .find(|l| l.contains("title=\"pdf\""))
+            .and_then(|l| {
+                let start = l.find("href=\"")? + 6;
+                let end = l[start..].find('"')? + start;
+                Some(l[start..end].to_string())
+            })
+            .unwrap_or_else(|| format!("https://arxiv.org/pdf/{arxiv_id}"));
+
+        out.push(Paper {
+            title: title.split_whitespace().collect::<Vec<_>>().join(" "),
+            summary: field("summary")
+                .unwrap_or_default()
+                .split_whitespace()
+                .collect::<Vec<_>>()
+                .join(" "),
+            published: field("published").unwrap_or_default(),
+            authors,
+            pdf_url,
+            arxiv_id,
+        });
+    }
+    out
+}
+
+fn unescape(s: &str) -> String {
+    s.replace("&amp;", "&")
+        .replace("&lt;", "<")
+        .replace("&gt;", ">")
+        .replace("&quot;", "\"")
+        .replace("&#39;", "'")
+}
+
+/// Search arXiv. `max_results` is capped to keep one run bounded.
+pub async fn search(query: &str, max_results: usize) -> Result<Vec<Paper>, String> {
+    let max = max_results.clamp(1, 50);
+    let url = format!(
+        "https://export.arxiv.org/api/query?search_query={}&start=0&max_results={max}\
+         &sortBy=submittedDate&sortOrder=descending",
+        urlencoding(query)
+    );
+    let body = reqwest::Client::new()
+        .get(&url)
+        .header("User-Agent", "clawmates-papers/0.1 (research library)")
+        .timeout(std::time::Duration::from_secs(60))
+        .send()
+        .await
+        .map_err(|e| format!("arxiv query: {e}"))?
+        .text()
+        .await
+        .map_err(|e| format!("arxiv body: {e}"))?;
+    Ok(parse_atom(&body))
+}
+
+/// Download the PDF. Returns the bytes; the caller decides where to shelve it.
+pub async fn fetch_pdf(paper: &Paper) -> Result<Vec<u8>, String> {
+    let bytes = reqwest::Client::new()
+        .get(&paper.pdf_url)
+        .header("User-Agent", "clawmates-papers/0.1 (research library)")
+        .timeout(std::time::Duration::from_secs(180))
+        .send()
+        .await
+        .map_err(|e| format!("fetch pdf {}: {e}", paper.arxiv_id))?
+        .bytes()
+        .await
+        .map_err(|e| format!("read pdf {}: {e}", paper.arxiv_id))?;
+
+    // A PDF starts with `%PDF`. arXiv serves an HTML holding page when a PDF
+    // is still rendering, and shelving that would leave a file that looks
+    // present and is unreadable.
+    if !bytes.starts_with(b"%PDF") {
+        return Err(format!(
+            "{} did not return a PDF ({} bytes, starts {:?})",
+            paper.pdf_url,
+            bytes.len(),
+            String::from_utf8_lossy(&bytes[..bytes.len().min(16)])
+        ));
+    }
+    Ok(bytes.to_vec())
+}
+
+/// The catalogue note for a shelved paper.
+///
+/// `source_id` in the frontmatter is the load-bearing part — it is what
+/// `corpus::parse_note` reads to rebuild the checkmark list from the vault.
+pub fn catalogue_note(paper: &Paper, blob_key: &str) -> String {
+    let authors = if paper.authors.is_empty() {
+        "unknown".to_string()
+    } else {
+        paper.authors.join(", ")
+    };
+    format!(
+        "---\n\
+         source_id: arxiv:{id}\n\
+         arxiv: {id}\n\
+         title: \"{title}\"\n\
+         authors: \"{authors}\"\n\
+         published: {published}\n\
+         pdf: {blob_key}\n\
+         url: https://arxiv.org/abs/{id}\n\
+         added: {added}\n\
+         tags: [paper, arxiv]\n\
+         ---\n\
+         \n\
+         # {title}\n\
+         \n\
+         **Authors:** {authors}  \n\
+         **arXiv:** [{id}](https://arxiv.org/abs/{id})  \n\
+         **PDF:** `{blob_key}`\n\
+         \n\
+         ## Abstract\n\
+         \n\
+         {summary}\n\
+         \n\
+         ## Notes\n\
+         \n\
+         _Catalogued automatically. Add your own notes below._\n",
+        id = paper.arxiv_id,
+        title = paper.title.replace('"', "'"),
+        authors = authors,
+        published = paper.published,
+        blob_key = blob_key,
+        added = paper.published,
+        summary = paper.summary,
+    )
+}
+
+fn urlencoding(s: &str) -> String {
+    s.bytes()
+        .map(|b| match b {
+            b'A'..=b'Z' | b'a'..=b'z' | b'0'..=b'9' | b'-' | b'_' | b'.' | b'~' => {
+                (b as char).to_string()
+            }
+            b' ' => "+".to_string(),
+            _ => format!("%{b:02X}"),
+        })
+        .collect()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    /// A revision must not read as a new paper.
+    #[test]
+    fn version_suffixes_are_stripped() {
+        assert_eq!(normalize_arxiv_id("http://arxiv.org/abs/2401.12345v3"), "2401.12345");
+        assert_eq!(normalize_arxiv_id("2401.12345v1"), "2401.12345");
+        assert_eq!(normalize_arxiv_id("2401.12345"), "2401.12345");
+        // Old-style ids contain letters and a slash.
+        assert_eq!(normalize_arxiv_id("http://arxiv.org/abs/cs/0701001"), "0701001");
+        // A trailing `v` with no digits is part of the id, not a version.
+        assert_eq!(normalize_arxiv_id("2401.1234v"), "2401.1234v");
+    }
+
+    /// Parsed against the real shape of arXiv's Atom feed. If this fails the
+    /// format drifted — which otherwise shows up as "no new papers", which is
+    /// indistinguishable from a quiet week.
+    #[test]
+    fn entries_are_parsed_from_a_real_feed() {
+        let xml = r#"<?xml version="1.0" encoding="UTF-8"?>
+<feed xmlns="http://www.w3.org/2005/Atom">
+  <entry>
+    <id>http://arxiv.org/abs/2401.12345v2</id>
+    <published>2026-01-15T10:00:00Z</published>
+    <title>Attention Is All You Need   Again</title>
+    <summary>  We show that
+    attention still works.  </summary>
+    <author><name>Ada Lovelace</name></author>
+    <author><name>Alan Turing</name></author>
+    <link href="http://arxiv.org/abs/2401.12345v2" rel="alternate" type="text/html"/>
+    <link title="pdf" href="http://arxiv.org/pdf/2401.12345v2" rel="related" type="application/pdf"/>
+  </entry>
+</feed>"#;
+        let papers = parse_atom(xml);
+        assert_eq!(papers.len(), 1);
+        let p = &papers[0];
+        assert_eq!(p.arxiv_id, "2401.12345", "version stripped");
+        assert_eq!(p.title, "Attention Is All You Need Again", "whitespace collapsed");
+        assert_eq!(p.summary, "We show that attention still works.");
+        assert_eq!(p.authors, vec!["Ada Lovelace", "Alan Turing"]);
+        assert_eq!(p.pdf_url, "http://arxiv.org/pdf/2401.12345v2");
+        assert_eq!(p.source_id(), "arxiv:2401.12345");
+        assert_eq!(p.blob_key(), "papers/arxiv/2401.12345.pdf");
+        assert_eq!(p.note_path(), "60 Papers/arxiv-2401.12345.md");
+    }
+
+    #[test]
+    fn an_empty_feed_yields_no_papers_rather_than_panicking() {
+        assert!(parse_atom("<feed></feed>").is_empty());
+        assert!(parse_atom("").is_empty());
+    }
+
+    #[test]
+    fn xml_entities_are_unescaped() {
+        let xml = r#"<feed><entry><id>http://arxiv.org/abs/1v1</id>
+        <title>Cats &amp; Dogs &lt;3</title><summary>a &quot;quote&quot;</summary>
+        </entry></feed>"#;
+        let p = &parse_atom(xml)[0];
+        assert_eq!(p.title, "Cats & Dogs <3");
+        assert_eq!(p.summary, "a \"quote\"");
+    }
+
+    /// The note must carry the identity `corpus::parse_note` reads, or the
+    /// catalogue cannot rebuild the checkmark list and the library forgets
+    /// itself the moment the database is lost.
+    #[test]
+    fn a_catalogue_note_round_trips_through_the_corpus_parser() {
+        let paper = Paper {
+            arxiv_id: "2401.12345".into(),
+            title: "A \"Quoted\" Title".into(),
+            authors: vec!["Ada Lovelace".into()],
+            summary: "Summary text.".into(),
+            published: "2026-01-15T10:00:00Z".into(),
+            pdf_url: "http://arxiv.org/pdf/2401.12345".into(),
+        };
+        let note = catalogue_note(&paper, &paper.blob_key());
+
+        let parsed = crate::corpus::parse_note(&paper.note_path(), &note);
+        assert_eq!(
+            parsed.declared_source_id.as_deref(),
+            Some("arxiv:2401.12345"),
+            "the corpus parser must recover the identity from the note"
+        );
+        assert_eq!(parsed.title.as_deref(), Some("A 'Quoted' Title"));
+        assert!(note.contains("papers/arxiv/2401.12345.pdf"), "note points at the shelf");
+    }
+
+    #[test]
+    fn queries_are_url_encoded() {
+        assert_eq!(urlencoding("all:agent topologies"), "all%3Aagent+topologies");
+    }
+}

crates/cm-api/tests/corpus_vault.rs

@@ -199,3 +199,30 @@ async fn index_the_real_vault() {
     assert_eq!(b.updated, 0);
     assert_eq!(b.unchanged, a.scanned);
 }
+
+/// Live arXiv check. Ignored by default (needs network); run with
+/// `cargo test -p cm-api --test corpus_vault live_arxiv -- --ignored --nocapture`.
+///
+/// Guards the one failure that hides: if arXiv's feed format drifts, parsing
+/// returns zero papers, which looks exactly like "no new papers this week".
+#[tokio::test]
+#[ignore]
+async fn live_arxiv_search_and_fetch() {
+    let papers = cm_api::papers::search("all:agentic topologies", 3)
+        .await
+        .expect("arxiv search");
+    println!("found {} papers", papers.len());
+    assert!(!papers.is_empty(), "arXiv returned nothing — format drift?");
+
+    for p in &papers {
+        println!("  {} | {}", p.source_id(), &p.title[..p.title.len().min(60)]);
+        assert!(!p.arxiv_id.is_empty());
+        assert!(!p.title.is_empty());
+        assert!(!p.arxiv_id.contains('v'), "version must be stripped: {}", p.arxiv_id);
+    }
+
+    let pdf = cm_api::papers::fetch_pdf(&papers[0]).await.expect("fetch pdf");
+    println!("pdf bytes: {}", pdf.len());
+    assert!(pdf.starts_with(b"%PDF"));
+    assert!(pdf.len() > 10_000, "suspiciously small pdf: {}", pdf.len());
+}