archive-fallback

Codifies the AGENTS.md retry policy: "If an API fails twice, switch to fallback
strategy immediately — don't keep retrying the same endpoint."

Decision ladder

For each target URL, walk in order. Stop at first success.

Level 1 — IIIF manifest

Probe canonical IIIF entry points. If the archive exposes a manifest, fetch
the highest-resolution derivative directly. No Playwright cost.

• Gallica: https://gallica.bnf.fr/iiif/ark:/<ark>/manifest.json
• Europeana: via API record/<dataset>/<id>.json → edmIsShownBy
• LOC: https://www.loc.gov/item/<id>/?fo=json

Use $REPO/tools/scripts/gallica_discovery.py when target is Gallica.

Level 2 — Direct HTTP, 2 retries max

backoff = [2, 8]  # seconds
for attempt, wait in enumerate(backoff, 1):
    resp = fetch(url)
    if resp.ok: return resp
    if resp.status in (429, 503):
        sleep(wait)
        continue
    break  # hard failure — do not retry

Never exceed 2 retries on the same endpoint.

Level 3 — Playwright bypass

For archives behind JS/anti-bot (Colnect, some Numista pages):

conda run -n iconocracy python -c "
from playwright.sync_api import sync_playwright
with sync_playwright() as p:
    browser = p.chromium.launch()
    page = browser.new_page()
    page.goto(url, wait_until='networkidle')
    # capture the <img> src or screenshot the target region
"

Timeout 30s per page. Do not retry at this level.

Level 4 — Metadata-only fallback

If all fetch attempts fail:

1. Create vault/candidatos/XX-NNN Title.md using existing vault naming
   pattern with whatever metadata was gathered (title, date, holding
   institution, source URL).
2. Tag #imagem-pendente and #verificar.
3. Append to $REPO/vault/sessoes/archive-failures-YYYY-MM-DD.md (ISO date).
   Line format:

   - SCOUT-NNN | <url> | <last-error> | attempts: IIIF/HTTP/PW

4. Do NOT write a placeholder image file. Corpus entries without an image
   stay text-only until a future campaign resolves them.

Report format

After a batch:

| SCOUT  | Level reached | Status              |
|--------|---------------|---------------------|
| FR-042 | 1 (IIIF)      | OK                  |
| FR-043 | 2 (HTTP)      | OK after 1 retry    |
| DE-019 | 3 (Playwright)| OK                  |
| BR-008 | 4 (metadata)  | pendente            |

Integration points

• SCOUT (the scout/buscar mode in AGENTS.md mode routing) calls this
  sub-routine whenever requests.get raises, times out, or returns non-2xx.
• ARGOS (tools/scripts/argos_build_manifest.py) consumes the failure log
  from vault/sessoes/archive-failures-*.md to rebuild the acquisition manifest.

Do NOT

• Keep retrying the same endpoint past Level 2 — violates AGENTS.md policy.
• Synthesize or hallucinate missing image data.
• Save binary placeholders to data/raw/ (ADR-001 + CI will reject).