fix: avoid npm reinstall for empty devDependencies

[harsh21234i]

Summary

• Treat a missing devDependencies field and an empty object as equivalent when comparing rendered package manifests.
• Preserve the npm install cache when a source-only reload produces no meaningful manifest change.
• Add regression tests for manifest sync and install-cache preservation.

Fixes #7480

Tests

• uv run pytest tests/units/utils/test_frontend_skeleton.py tests/units/utils/test_js_runtimes.py -q (24 passed)
• Targeted pre-commit checks passed.
• Verified locally with REFLEX_USE_NPM=1: a Python source-only hot reload rebuilt the app without rerunning npm install.

[cubic-dev-ai]

No issues found across 3 files

_{View guided diff | Re-trigger cubic}

[greptile-apps]

Confidence Score: 5/5

[Medium impact] The PR appears safe to merge.

Summary

Treats missing and empty devDependencies as equivalent so source-only reloads avoid unnecessary npm installs.

• An empty devDependencies field no longer triggers a frontend reinstall.

_{Reviews (4) · Last reviewed commit: "Merge remote-tracking branch 'upstream/m..." · Reviewed by Greptile}

[codspeed]

Merging this PR will improve performance by 4.12%

⚠️ 17 benchmarks spent significant time in system calls

System calls cannot be consistently instrumented, so they are not included in the measure, which understates the real cost. Please switch to the Walltime instrument to accurately measure system calls.

Measurement and system calls

• test_cli_startup[version]
• test_cli_startup[help]
• test_state_manager_memory_read_only_modify
• test_state_manager_memory_modify
• test_state_manager_memory_cold_get
• test_import_cli
• test_get_state[disk]
• test_modify_state[disk]
• test_set_state[disk]
• test_event_shutdown_cancel
• …and 7 more

⚠️ Different runtime environments detected

Some benchmarks with significant performance changes were compared across different runtime environments,
which may affect the accuracy of the results.

Open the report in CodSpeed to investigate

⚡ 1 improved benchmark
✅ 147 untouched benchmarks

Performance Changes

	Benchmark	BASE	HEAD	Efficiency
⚡	test_route_argument_extraction	119.7 µs	114.9 µs	+4.12%

Tip

Curious why performance improved? Comment @codspeedbot explain why performance improved on this PR, or directly use the CodSpeed MCP with your agent.

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_{Comparing harsh21234i:fix/7480-npm-manifest-normalization (f35ef79) with main (7ccaa4e)}