Spike: diagnose or replace dslipak/pdf (uninterruptible hang → DoS vector)

[dratner]

Background

extract/pdf (landed in #6) uses github.com/dslipak/pdf. Testing surfaced a concrete failure: a structurally-valid PDF whose single page has no /Contents stream parses fine (NumPage()==1, page not null) but then GetPlainText hangs — it spins without returning.

This is worse than the panics the original Morris design anticipated:

• recover() cannot catch a hang, so the panic-recovery boundary is useless against it.
• The parser ignores context cancellation (no ctx awareness), so a caller cannot interrupt it cooperatively.

For a library that accepts untrusted PDFs, an uninterruptible hang is a denial-of-service vector: one crafted input ties up a worker indefinitely.

Current stopgap (shipped in #6, ADR 0007)

extract/pdf ships a wall-clock timeout watchdog (Extractor.Timeout, default 30s): parsing runs in a goroutine, Extract selects on result / ctx.Done() / timer, and returns extract.ErrMalformedSource on timeout.

This is knowingly a band-aid, not a fix:

• A timed-out parse leaks its goroutine — the worker stays stuck in the uninterruptible parser, so sustained hostile input grows memory. (Residual risk this stopgap does not close.)
• The timeout is wall-clock, conflating "hostile hang" with "legitimately huge PDF".

Spike goals

• Diagnose the hang — is it specifically the missing-/Contents case? Can we pre-validate page structure to avoid it, or is it fixable upstream?
• Evaluate maintained alternatives to dslipak/pdf.
• Decide on out-of-process parsing — the real fix for an uninterruptible parser (sandbox / separate process with hard kill).

Outcome supersedes ADR 0007.

Until then

Do not point extract/pdf at high-volume untrusted input without external process isolation.

References

• ADR 0007 — docs/adr/0007-pdf-extraction-watchdog-stopgap.md
• docs/deferred-tooling.md Phase 1: chunk — boundary-aware chunker with token-budget enforcement #4
• PR extract/pdf + extract/docx (PDF ships with a hang watchdog — needs your eyes) #6