fix(dev): let a restarted fork reload changed .env values

[productdevbook]

Editing .env during nuxt dev prints .env changed. Restarting Nuxt in a new process..., but the new process keeps serving the old values.

Cause

ForkPool.createFork passes { ...process.env } to the fork. By then the parent's process.env already contains whatever the previous .env set.

setupDotenv in c12 only overwrites a variable when it is undefined or when c12 set it itself, and it tracks which ones it set in globalThis.__c12_dotenv_vars__. That record is per process, so inside the fork the stale values look like real shell variables. The fresh .env never wins: a changed value is ignored, and a removed one stays.

Fix

Before forking, drop the variables that c12 recorded as set by .env files in this process (withoutDotenvVars in dev/pool.ts). The fork then loads .env from scratch. Variables that came from the shell are not in that record, so they are passed through unchanged. If the record is missing (another c12), the env is passed as before.

Reproduction

The fixture's nuxt.config.ts has runtimeConfig: { public: { benchMarker: '' } }, and the dev server runs with CI=1:

echo NUXT_PUBLIC_BENCH_MARKER=before > .env
nuxt dev --port 33992 &
curl -s localhost:33992/ | grep -o 'public:{[^}]*}'   # public:{benchMarker:"before"}
echo NUXT_PUBLIC_BENCH_MARKER=after > .env           # ".env changed. Restarting Nuxt in a new process..."
curl -s localhost:33992/ | grep -o 'public:{[^}]*}'

	after the 1st edit (after)	after the 2nd edit (third)
main	benchMarker:"before" ❌	—
this PR	benchMarker:"after" ✅	benchMarker:"third" ✅

Checks

• eslint and tsc --noEmit pass
• vitest run packages/nuxt-cli/test/unit plus e2e dev-restart and dev: 134 files, 1881 tests passed

🤖 Generated with Claude Code

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ℹ️ Recent review info

⚙️ Run configuration

• Configuration used: Organization UI
• Review profile: CHILL
• Plan: Advanced
• Run ID: 3e479945-7691-4846-a53d-c8f8f1fa676f

📥 Commits

Reviewing files that changed from the base of the PR and between f140924 and afea75d.

📒 Files selected for processing (2)

• packages/nuxt-cli/src/dev/pool.ts
• packages/nuxt-cli/test/e2e/dev-dotenv.spec.ts

Included review availability: This review used your included allowance. Your plan provides up to 2 included reviews per hour; 1 remain after this review.

---

📝 Walkthrough

Walkthrough

The dev pool now removes registered dotenv keys from the environment passed to forked processes. An end-to-end test checks that dotenv updates change the returned marker, the shell-provided value remains unchanged, and the server PID changes after each update.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~12 minutes

Merge Risk: ⚪ Minimal · up to afea7

Restarted dev forks now reload changed .env values while keeping shell-provided variables. No merge-blocking risk was identified.

Security Architecture Review

Security architecture risk: 🔵 Low · up to afea7

The change is limited to development-server restarts and preserves shell-provided settings in the inspected implementation. No introduced security issue was established. Remaining uncertainty concerns environment-ownership compatibility and settings modified by third-party code.

Retained concerns
No architecture-level concerns identified.

Security review details

Security Blast Radius

• inferred — The direct exposure is the development process family and application behavior driven by its environment. The inspected change does not grant a new identity or privilege; downstream effects depend on the application’s existing use of configuration and credentials.

Trust Boundaries and Controls

• inferred — Dotenv remains an existing configuration input rather than a newly exposed remote source. The changed boundary prevents inherited dotenv values from being mistaken for shell-authoritative values in the child. Preservation of shell authority is supported for the inspected registry implementation, not every dependency variant or later external mutation.

Resilience and Maintainability Implications

• observed — Fork cleanup is guarded against repetition and escalates from graceful shutdown to termination. Failed handover intentionally retains the old configuration; the PR does not make configuration replacement atomic across startup failure.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 50.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 4 functions across 2 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly describes the main change: allowing restarted dev-server forks to reload updated .env values.
Description check	✅ Passed	The description explains the stale .env value problem, its cause, the fix, and how to reproduce it. It matches the changeset.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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[pkg-pr-new]

• nuxt-cli-playground

  npm i https://pkg.pr.new/create-nuxt@1592
  

  npm i https://pkg.pr.new/nuxi@1592
  

  npm i https://pkg.pr.new/@nuxt/cli@1592
  

commit: afea75d

[github-actions]

CLI benchmark

@nuxt/cli v4.0.0-alpha.1 (baseline) vs v4.0.0-alpha.1 (this PR)

Metric	baseline v4.0.0-alpha.1	head v4.0.0-alpha.1	Delta
nuxt --version wall time (median)	53 ms	54 ms	+2.5%
nuxt --help wall time (median)	107 ms	109 ms	+1.7%
nuxt dev --help wall time (median)	84 ms	84 ms	-0.4%
nuxt --version modules loaded	35	35	0.0%
nuxt --version built-ins loaded	27	27	0.0%
nuxt --help modules loaded	134	135	+0.7%
nuxt --help built-ins loaded	87	87	0.0%
nuxt dev --help modules loaded	63	64	+1.6%
nuxt dev --help built-ins loaded	87	87	0.0%
Installed node_modules	2.45 MB	2.45 MB	+0.2%
Published tarball (packed)	239.6 kB	240.9 kB	+0.5%

Full report

@nuxt/cli v4.0.0-alpha.1 (baseline) vs v4.0.0-alpha.1 (head)

Setting	Value
Baseline	ref:f140924fb88992febb831316ac01bce275609336 (v4.0.0-alpha.1)
Head	local packages/nuxt-cli at 59414c4 (v4.0.0-alpha.1)
Node	v24.21.0
OS	Linux 6.17.0 (kernel 6.17.0-1022-azure)
CPU	AMD EPYC 9V74 80-Core Processor x 4
Memory	15.6 GB
Load average at start	2.29, 0.63, 0.22
Run started	2026-10-05T14:31:05.637Z

Cold CLI startup

Median of 15 interleaved runs per command, one warmup discarded.

Command	baseline v4.0.0-alpha.1 median	head v4.0.0-alpha.1 median	Delta	baseline v4.0.0-alpha.1 min / p95	head v4.0.0-alpha.1 min / p95
nuxt --version	53 ms	54 ms	+2.5%	51 ms / 55 ms	51 ms / 56 ms
nuxt --version (first output byte)	49 ms	50 ms	+2.9%	47 ms / 52 ms	47 ms / 52 ms
nuxt --help	107 ms	109 ms	+1.7%	104 ms / 116 ms	105 ms / 113 ms
nuxt --help (first output byte)	103 ms	104 ms	+1.7%	99 ms / 111 ms	101 ms / 108 ms
nuxt dev --help	84 ms	84 ms	-0.4%	80 ms / 88 ms	80 ms / 88 ms
nuxt dev --help (first output byte)	80 ms	80 ms	-0.5%	76 ms / 84 ms	76 ms / 84 ms
nuxt <unknown-command> (no-op)	117 ms	116 ms	-0.2%	111 ms / 120 ms	111 ms / 120 ms
nuxt <unknown-command> (no-op) (first output byte)	112 ms	111 ms	-0.4%	106 ms / 115 ms	106 ms / 115 ms

Module load cost

Counted with a module.registerHooks load hook, compile cache disabled. Counts every JS module actually evaluated on that code path (native addons excluded). Built-ins loaded after bootstrap are counted separately, including the internal modules they load.

Command	baseline v4.0.0-alpha.1 modules	head v4.0.0-alpha.1 modules	Delta	baseline v4.0.0-alpha.1 source bytes	head v4.0.0-alpha.1 source bytes	Delta	baseline v4.0.0-alpha.1 built-ins	head v4.0.0-alpha.1 built-ins	Delta
nuxt --version	35	35	0.0%	297.8 kB	297.8 kB	0.0%	27	27	0.0%
nuxt --help	134	135	+0.7%	842.5 kB	847.4 kB	+0.6%	87	87	0.0%
nuxt dev --help	63	64	+1.6%	453.0 kB	455.3 kB	+0.5%	87	87	0.0%

Install footprint and published tarball

Each version installed on its own into an empty project with nothing but @nuxt/cli as a dependency, so the tree is exactly the CLI and its transitive dependencies. npm cache is warm and the registry is only consulted for metadata, so install wall time is indicative, not a network benchmark.

Metric	baseline v4.0.0-alpha.1	head v4.0.0-alpha.1	Delta
Direct dependencies of @nuxt/cli	23	23	0.0%
Packages in the installed tree (unique name@version)	39	39	0.0%
Unique package names	39	39	0.0%
Package directories on disk (cross-check)	32	32	0.0%
Installed node_modules on disk	2.45 MB	2.45 MB	+0.2%
Installed files	434	435	+0.2%
Install wall time (warm npm cache, median of 3)	996 ms	1.01 s	+1.9%
Published tarball (packed)	239.6 kB	240.9 kB	+0.5%
Published tarball (unpacked)	775.2 kB	779.8 kB	+0.6%
Files in tarball	99	100	+1.0%

Interleaved runs on a shared runner: trust the deltas, not the absolute timings. The dev, restart and build suites run locally via pnpm bench:cli.

[codspeed]

Merging this PR will not alter performance

✅ 2 untouched benchmarks

---

_{Comparing productdevbook:fix/dev-fork-dotenv (afea75d) with main (435c41f)}

[codecov-commenter]

Codecov Report

❌ Patch coverage is 80.00000% with 1 line in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (main@f140924). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
packages/nuxt-cli/src/dev/pool.ts	80.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1592   +/-   ##
=======================================
  Coverage        ?   83.46%           
=======================================
  Files           ?      177           
  Lines           ?    11371           
  Branches        ?     3267           
=======================================
  Hits            ?     9491           
  Misses          ?     1584           
  Partials        ?      296           

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