pandoc --pdf-engine fails with "openFile: resource busy (file is locked)" on deployed Containers — the tutorial's PDF flow cannot work in production

コミット 76d9e75 のデプロイ済み examples/container reproduction とその Dockerfile から始め、次に、一覧にある /c/repro1/exec と file-sync のプローブを実行して、wrangler dev とデプロイ済みの Container を比較します。チュートリアルの pandoc --pdf-engine フローが引き続き壊れているか、また、文書化されている pandoc-to-typst の stdout 回避策が成功するかを確認します。完了の条件は、本番の PDF パスが動作するか、チュートリアルが制限事項と回避策を明確に文書化していることです。

Summary

The PDF-conversion flow the tutorial documents (pandoc card.md -o card.pdf --pdf-engine=typst) fails on real, deployed Cloudflare Containers with:

pandoc: openFile: resource busy (file is locked)
HasCallStack backtrace:
  bracket, called at ./System/IO/Temp.hs:114:3 in temporary-1.3-…:System.IO.Temp

The same command works under wrangler dev (local Docker), so the failure is invisible until first deploy. The trigger is narrow: it is specifically the --pdf-engine path's temp-file staging (System.IO.Temp / the temporary package, i.e. GHC's file locking on the temp file). Plain pandoc output files and ordinary shell writes to the same filesystem are fine.

Reproduction

examples/container from this repo at 76d9e75, deployed unmodified except for two Dockerfile changes: computerd tag bumped to 0.1.1 (to match the published @cloudflare/computer@0.1.1 the example was installed with), and pandoc 3.10.1 + typst 0.15.1 added to the image (same tools the tutorial uses). wrangler 4.119, instance type standard-2.

All probes are plain curl against the deployed example's own HTTP surface:

Control — the filesystem accepts writes (shell):

POST /c/repro1/exec {"command":"sh -c 'echo ctrl > /tmp/ctrl.txt && cat /tmp/ctrl.txt'"}
→ {"status":"completed","exitCode":0,"stdout":"ctrl\n"}

Control — plain pandoc output file works (no engine involved):

POST /c/repro1/exec {"command":"printf \"# hi\\n\" | pandoc -f markdown -t docx -o /tmp/out.docx -"}
→ {"status":"completed","exitCode":0}

Failure — any --pdf-engine invocation, container-local /tmp:

POST /c/repro1/exec {"command":"printf \"# hi\\n\" | pandoc -f markdown -o /tmp/out.pdf --pdf-engine=typst -"}
→ {"status":"failed","exitCode":1,"stderr":"pandoc: openFile: resource busy (file is locked)\nHasCallStack backtrace:\n  bracket, called at ./System/IO/Temp.hs:114:3 …"}

Failure — the tutorial's exact flow (input written host-side, synced to the mount — note pushed: 2, sync itself works fine):

PUT  /c/repro1/file/workspace/card.md  ("# Karta…")
POST /c/repro1/exec {"command":"pandoc /workspace/card.md -o /workspace/card.pdf --pdf-engine=typst"}
→ {"status":"failed","exitCode":1,"stderr":"pandoc: openFile: resource busy (file is locked)…","pushed":2,"sync":{"status":"complete","applied":3}}

Analysis

GHC takes an fcntl lock when System.IO.Temp opens the temp file that the --pdf-engine path stages the intermediate document into, and the deployed Container filesystem refuses that lock (EBUSY-shaped failure surfaced as "resource busy (file is locked)"). Local Docker's filesystem grants the lock, hence the dev/prod split. Ordinary openFile for pandoc's --output does not trip it (the docx control above), so the blast radius is exactly "anything that goes through pandoc's PDF-engine temp staging".

Working workaround (verified on the same deployment)

Skip --pdf-engine entirely: have pandoc emit standalone typst markup to stdout (shell owns the file), then compile with typst (Rust — no GHC locking):

POST /c/repro1/exec {"command":"printf \"# hi\\n\" | pandoc -f markdown -t typst -s - > /tmp/x.typ && typst compile /tmp/x.typ /tmp/x.pdf && ls -la /tmp/x.pdf"}
→ {"status":"completed","exitCode":0,"stdout":"-rw-r--r-- 1 root root 7004 … /tmp/x.pdf\n"}

Possibly worth a note in the tutorial until the underlying lock behavior is addressed on the Containers filesystem — as-is, the tutorial's flagship command works in every local run and fails on the first production deploy, which is an expensive way to find out.

Happy to provide the deployed-example wrangler config or run further probes if useful.