cp-skill-snapshot-web

# Known Limitations

## Client-rendered and access-controlled pages may have no extractable HTML

The ordinary-page pathway downloads and extracts the page with Trafilatura. It
does not execute JavaScript, authenticate, or bypass a paywall. A
client-rendered page, login wall, bot challenge, or error shell may therefore
yield no substantive content.

**How to detect:** Trafilatura produces an empty result or extracts only an
access message or application shell. Compare the result with the
browser-visible source before treating a short extraction as complete.

## Image-only PDFs require OCR

Poppler's `pdftotext` extracts text embedded in a PDF. A scanned or image-only
PDF may produce an empty file even when every page is visually readable. The
snapshot workflow has no OCR prerequisite or fallback; provide an OCR-produced
text copy or paste the content manually.

## PDF snapshots preserve extraction artifacts

The PDF pathway copies `pdftotext` output into the snapshot without requiring
the model to re-emit the document. The `-nopgbrk` option removes page-break
characters, but repeated page headers, line-break hyphenation, flattened
tables, and degraded equation glyphs may remain. This is a faithful,
completion-safe capture rather than polished Markdown. Cleanup is a separate
bounded transformation so a blocked model write cannot prevent capture.

---
name: cp-skill-snapshot-web
description: Snapshot a URL into the local kb/sources/.snapshots/ cache, routing GitHub, X/Twitter, PDF, and ordinary web sources to the appropriate capture path.
type: kb/types/instruction.md
user-invocable: true
allowed-tools: Read, Write, Grep, Glob, Bash
context: fork
model: sonnet
argument-hint: "[url] — URL to snapshot (web page, PDF, GitHub issue/PR, or X/Twitter post)"
---

## EXECUTE NOW

**Target: $ARGUMENTS**

If no URL provided, ask the user for one.

If URL provided, start Step 1 immediately.

**START NOW.**

---

## Step 1: Verify Local Storage and Check for Duplicates

Keep the provided URL as `source_url`. Verify that
`kb/sources/.snapshots/` is ignored by the project. The shipped scaffold does
this through `kb/sources/.gitignore`. If the directory is not ignored, stop
before writing and report the missing rule.

Use Grep to search for an exact frontmatter `source: {source_url}` in existing
Markdown files in `kb/sources/.snapshots/`. If found, compute the SHA-256 of
the exact file bytes, tell the user, and stop:

> Already snapshotted: kb/sources/.snapshots/{filename}
> SHA-256: {64-character lowercase checksum}

## Step 2: Route by URL Type

Detect the `source_url` type and branch:

- **GitHub issue/PR** (`github.com/.../issues/N` or `github.com/.../pull/N`) → **Step 2a**
- **X/Twitter** (`x.com/.../status/...` or `twitter.com/.../status/...`) → **Step 2b**
- **arXiv abstract page** (`arxiv.org/abs/...`) → **Step 2c**
- **PDF** (URL ends in `.pdf`, or `arxiv.org/pdf/`) → **Step 2c**
- **Everything else** → **Step 2d**

### Step 2a: GitHub Issue/PR

Run:

```bash
commonplace-github-snapshot "{source_url}"
```

Parse either the `Snapshot saved:` or `Already snapshotted:` line from the
output to get the file path. Tell the user and stop — the script handles
metadata, formatting, and saving.

### Step 2b: X/Twitter Post

Run:

```bash
commonplace-x-snapshot "{source_url}"
```

Parse either the `Snapshot saved:` or `Already snapshotted:` line from the
output to get the file path. Tell the user and stop — the script handles
metadata, formatting, and saving.

### Step 2c: Resolve and Fetch PDF

Verify that the PDF capture prerequisites are available:

```bash
command -v curl
command -v pdfinfo
command -v pdftotext
```

If any command is missing, go to **Step 3**. Do not probe for an alternative
converter.

Set `pdf_url`:

- For an arXiv abstract URL, replace `/abs/` with `/pdf/` and discard any query string or fragment. Preserve an explicit terminal version such as `v1`. If the abstract URL has no terminal version, leave the PDF URL unversioned so arXiv serves the latest paper version. For example, `https://arxiv.org/abs/2606.03979` becomes `https://arxiv.org/pdf/2606.03979`. Do not route the abstract page through ordinary HTML capture.
- For an existing PDF URL, use `source_url` unchanged.

Run this as one Bash invocation. Retain the printed directory path as
`{snapshot_tmp}`:

```bash
set -e
snapshot_tmp=$(mktemp -d)
printf 'Snapshot temp: %s\n' "$snapshot_tmp"
curl -fsSL -o "$snapshot_tmp/source.pdf" "{pdf_url}"
pdfinfo -isodates "$snapshot_tmp/source.pdf" > "$snapshot_tmp/pdfinfo.txt"
pdfinfo -meta "$snapshot_tmp/source.pdf" > "$snapshot_tmp/pdfmeta.xml" || true
pdftotext -enc UTF-8 -eol unix -nopgbrk \
  "$snapshot_tmp/source.pdf" "$snapshot_tmp/extracted.txt"
```

Use Read to inspect `pdfinfo.txt`, non-empty `pdfmeta.xml`, and a bounded
beginning of `extracted.txt`. DOI metadata inspection is best effort and its
failure does not make an otherwise successful capture fail. Treat PDF metadata
fields as leads, not as authority: confirm the title and authors against the
document text when available. Use Grep plus bounded Read ranges to locate an
abstract, executive summary, introduction, or the source document's own DOI
when the beginning does not supply enough metadata. Do not treat a DOI found
only in the references as the paper's DOI. Do not read the whole extracted
file merely to copy it. If `extracted.txt` is empty or contains no substantive
text, go to **Step 3**.

Set `capture_method` to `pdftotext`, set `body_file` to
`{snapshot_tmp}/extracted.txt`, and go to **Step 4**.

### Step 2d: Fetch Web Page

Verify that the HTML capture prerequisites are available:

```bash
command -v trafilatura
```

If the command is missing, go to **Step 3**. Do not probe for another HTML
converter.

Run this as one Bash invocation to download and extract the page. Retain the
printed directory path as `{snapshot_tmp}`:

```bash
set -e
snapshot_tmp=$(mktemp -d)
printf 'Snapshot temp: %s\n' "$snapshot_tmp"
trafilatura -u "{source_url}" \
  --markdown --with-metadata --links --no-comments --recall \
  --backup-dir "$snapshot_tmp/raw" \
  > "$snapshot_tmp/extracted.md"
```

Use Read to inspect only the leading metadata and a bounded beginning of
`extracted.md`. Its leading YAML block, when present, is Trafilatura metadata:
retain it as input to Step 4 but do not copy that block into the snapshot body.
Trafilatura also retains its downloaded HTML as a gzip file under
`{snapshot_tmp}/raw/`. When `gzip` is available, decompress that file within
`{snapshot_tmp}` and use Grep with bounded output to inspect article-level DOI
metadata such as `citation_doi`, `dc.identifier`, `prism.doi`, or a JSON-LD
`doi` property. DOI inspection is best effort: inability to inspect the raw
HTML does not make an otherwise successful capture fail.
Strip that block locally without re-emitting the document:

```bash
awk '
NR == 1 && $0 == "---" { in_metadata = 1; next }
in_metadata && $0 == "---" { in_metadata = 0; next }
!in_metadata { print }
' "{snapshot_tmp}/extracted.md" > "{snapshot_tmp}/body.md"
```

If `body.md` is empty or contains no substantive main content, go to
**Step 3**.

Set `capture_method` to `trafilatura`, set `body_file` to
`{snapshot_tmp}/body.md`, and go to **Step 4**.

## Step 3: Handle Failures

If any fetch or extraction method fails (missing prerequisite, curl error,
empty Trafilatura result, or PDF with no embedded text):

- Tell the user exactly what happened.
- For a missing prerequisite, name the canonical installation:
  - `trafilatura`: `uv tool install "trafilatura>=2.2"`
  - `pdfinfo` or `pdftotext`: install Poppler (`poppler-utils` on
    Debian/Ubuntu, `poppler` through Homebrew, or
    `oschwartz10612.Poppler` through WinGet)
  - `curl`: install curl
- For an image-only PDF, say that this workflow has no OCR fallback.
- Suggest they paste the content manually: "You can paste the text and I'll save it as a snapshot"
- Remove `{snapshot_tmp}` if one was created.
- Stop.

## Step 4: Determine Metadata

**(Only for PDF and web page paths — GitHub and X scripts handle their own metadata.)**

This workflow supplies `kb/sources/types/snapshot.md` as the type. Open that path and verify from its own frontmatter that it is a type spec before determining metadata. Stop if it is missing or invalid.

From the bounded excerpts, extractor metadata, and `source_url`, determine:

- **title**: The article/post title. Use the first H1 if present, otherwise derive from content.
- **author**: If identifiable from the content or URL (e.g. simonwillison.net → Simon Willison)
- **doi**: For a scholarly article or paper, try to identify the DOI from the
  `source_url`, extractor or document metadata, and the document's own title or
  citation block. Store the bare identifier beginning with `10.`; remove a
  leading `https://doi.org/` or `doi:` label and surrounding whitespace. Accept
  a candidate only when the source identifies it as the DOI of the captured
  work. A DOI found only in references is not sufficient. If candidates
  conflict or none is attributable to the captured work, omit `doi`; never
  guess or manufacture one.
- **genre**: the source's genre per the snapshot type spec's vocabulary. This is a surface judgment of what kind of document the source is as evidence — ingestion may correct it later. Prefer a value from the type spec's list; a value outside it validates with a warning, so extend only for a genuinely new evidential kind, not a container.
- **capture_scope**: `full-source`, `partial-source`, `abstract`, or `excerpt`
  under the snapshot type contract. Judge the retained body, not the success of
  the extraction command. In particular, label a publisher page that exposes
  only an abstract as `abstract`, even when that abstract is substantive.
- **description**: One sentence describing what makes this source worth retrieving. Not a summary — a retrieval filter (e.g. "Anthropic CEO's capability-timeline predictions — verifiable domains get confident timelines, unverifiable ones get hedged"). Focus on what distinguishes this source from others on the same topic.
- **slug**: Lowercase, hyphenated, max 63 chars. The paired ingest adds
  `.ingest` to the validated stem, so the snapshot basename must reserve those
  seven characters within the 70-character authored-artifact limit. Derive it
  from the title. Example: `simon-willison-karpathy-claws`.

For academic papers: prefer the title and complete author list printed in the
paper over `pdfinfo` or Trafilatura metadata.

## Step 5: Materialize the Snapshot

The extracted body must move from `body_file` to the snapshot through local
byte copying. Never place the whole source body in a Write or Edit call.

Use Write to create `{snapshot_tmp}/header.md` with this content and no source
body. End the file with the blank line after `Date`:

```markdown
---
source: {source_url}
description: {description}
captured: "{YYYY-MM-DD}"
capture: {capture_method}
capture_scope: {capture_scope}
genre: {genre}
doi: "{bare DOI; omit this line when no DOI was verified}"
type: kb/sources/types/snapshot.md
---

# {title}

Author: {author}
Source: {source_url}
DOI: {bare DOI; omit this line when no DOI was verified}
Date: {publication date if known}

```

Trafilatura has already produced the web body as Markdown. A PDF body remains
the complete plain text emitted by `pdftotext`; plain text is valid Markdown.
Do not make model-mediated PDF cleanup a condition of capture. If the user
explicitly requested cleanup, transform bounded chunks into a candidate body,
never send the whole document through one Write, and retain the raw
`extracted.txt` as fallback. Set `body_file` to the candidate only after every
source chunk is present and in order; otherwise keep the raw body.

Assemble the snapshot without sending the extracted bytes through model output:

```bash
set -e
snapshot_path="kb/sources/.snapshots/{slug}.md"
cp "{snapshot_tmp}/header.md" "$snapshot_path"
cat "{body_file}" >> "$snapshot_path"
header_bytes=$(wc -c < "{snapshot_tmp}/header.md")
body_bytes=$(wc -c < "{body_file}")
snapshot_bytes=$(wc -c < "$snapshot_path")
test "$snapshot_bytes" -eq "$((header_bytes + body_bytes))"
```

Compute SHA-256 after the file is complete. Hash the exact `.md` bytes,
including frontmatter, line endings, and the presence or absence of a final
newline. Do not include a PDF, JSON, image, or other capture companion. Tell
the user where the snapshot was saved, its lowercase checksum, and a one- or
two-line preview.

## Critical Constraints

**Never:**
- Fabricate or hallucinate content not on the page
- Add analysis or commentary — this is capture, not ingestion
- Re-emit a complete extracted body through Write or Edit
- Make model-mediated cleanup a prerequisite for saving a snapshot
- Save to any directory other than `kb/sources/.snapshots/`
- Install software — if a required tool is missing, bail with an error telling the user what to install

**Always:**
- Copy every `body_file` byte in order on the default capture path
- Include the source URL in frontmatter
- Use today's date for `captured`
- Check for duplicates before fetching
- Keep the snapshot and every capture companion local and ignored
- Remove the unique temporary download/extraction directory after the snapshot
  is written and hashed