@workflow/next: infinite rebuild loop when Next.js uses a custom distDir (watcher ignore list misses it) #2809

Summary

The Next.js plugin's file watcher hardcodes an ignore list (/.next/, /dist/, /build/, /.cache/, …) in packages/next (builder-eager.js, ignoredPathFragments). If a project sets a custom distDir in next.config — e.g. distDir: ".next-dev" for dev — the watcher does NOT ignore it. Every Next compile then re-triggers the workflow builder, whose writes re-trigger Next, producing an infinite rebuild loop.

Versions

• workflow 4.2.5, @workflow/next 4.0.6
• next 14.2.35, macOS (darwin arm64), next dev (webpack)

Mechanism

1. The plugin (re)builds and writes generated files under app/.well-known/workflow/v1/ (including an unconditional writeFile of config.json, so mtimes bump even when content is unchanged).
2. Next.js watches app/, recompiles, and writes compiler output to the custom distDir (.next-dev/ in our case).
3. The plugin's watchpack instance ignores /.next/ but not .next-dev/, sees the output change, and rebuilds → back to 1.

Observed impact

• ~0.5–1.5 rebuild cycles/sec continuously while next dev runs; one 2.5 h session logged 14,080 "Discovering workflow directives / Created steps bundle" cycles.
• Each cycle triggers Fast Refresh; with a dashboard tab open on a force-dynamic server-component page, its data reads re-ran continuously — we measured 620 Redis commands/min from a single idle browser tab, which exhausted an Upstash free-tier monthly quota (500k requests) in a few days of normal development.
• Constant CPU churn from the compile loop even with no tab open.

Repro

1. next.config.mjs: distDir: process.env.NODE_ENV === "development" ? ".next-dev" : ".next"
2. Any project with the workflow Next plugin enabled; run next dev.
3. Watch the terminal: Discovering workflow directives → Created steps bundle → ✓ Compiled → … repeats forever with no source changes.

Renaming the dev distDir to .cache/next-dev (a fragment the hardcoded list happens to ignore) stops the loop immediately (0 rebuilds over 90 s, was ~50–100).

Suggested fixes

• Read the resolved distDir from the Next config and add it to the watcher's ignore list, rather than relying on hardcoded names.
• Independently: skip the write when generated file content is unchanged (compare before writeFile), which would break the cycle even for unknown watched paths.

🤖 Filed with Claude Code