feat: direct system-defaults apply path, fix found issues in the existing system-defaults defs

[Scott McMaster (scottmcmaster)]

Summary

The main business purpose of this change is to wire the system defaults edits up directly rather than applying them through the agent prompt. That wiring was actually more straightforward than I expected from the existing code. But when I started trying to build some actual changes based on this, I ran into other issues I had to fix:

• One option value is exposed by defaults as an int but defined as a string in nix-darwin. So I added a new ValType for mappings and updated the KeyDefs as appropriate.
• This got me thinking, so I added a flag you can change in the code that will force nixmac to detect "drift" on ALL the available defaults. And when I did that, sure enough:
• Several other things would not nix-eval properly. Mostly things defined as int's that were really supposed to be nullable bool's. So I fixed all those.

As of right now, then, everything is at least plausible enough to pass through nix-eval, although I think we need to have more discussion about how we maintain this code. I'll open that up separately.

Test Plan

Some minor unit test changes, and lots of manual testing including the aforementioned new code-based way to make sure that every option is typed correctly in the KeyDefs.

• No test plan needed

Docs

• Docs updated (companion PR in darkmatter/nixmac-web: #___)
• No docs update needed

[Scott McMaster (scottmcmaster)]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• feat: direct system-defaults apply path, fix found issues in the existing system-defaults defs #406 👈 (View in Graphite)
• feat: use real system defaults scanner to populate items on the filesystem untracked tab #404
• feat: use real homebrew untracked diff in filesystem view #403
• feat: add homebrew_add_casks managed-edit command and wire up direct tracking in the filesystem UI #393
• develop

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[github-actions]

📋 PR Overview

Lines changed	414 (+359 / -55)
Files	0 added, 6 modified, 0 deleted
Draft / WIP	no
Has Test Plan	yes
No Test Plan Needed	no
New UI components	no
New Storybook stories	no
New Rust modules	no
New TS source files	no
New tests	no
package.json touched	no
Cargo.toml touched	no
Infra / CI touched	no

🔬 Coverage

Report	Lines	Statements	Functions	Branches
apps/native/coverage/coverage-summary.json	25.8%	26.0%	25.0%	18.9%

Generated by 🚫 dangerJS against 63056fd

[Copilot]

Pull request overview

This PR wires “system defaults” untracked items into a direct managed-edit apply flow (similar to Homebrew), rather than routing through prompt seeding, and hardens the macOS defaults scanner so its generated Nix matches nix-darwin option types (including null defaults and int→string mappings).

Changes:

• Added a refreshable useSystemDefaultsScan hook and used it to re-scan after applying defaults.
• Extended the Filesystem “Untracked” UI to support a direct “track/apply” path for system defaults candidates.
• Updated the Rust system-defaults scanner typing/comparison and Nix generation (null sentinel + int→string mapping support), plus unit tests.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
apps/native/src/hooks/use-system-defaults-scan.ts	Adds a memoized refresh() API and exposes it to callers.
apps/native/src/components/widget/filesystem/untracked-card.tsx	Routes “Track” actions to system-defaults direct apply when applicable, otherwise falls back to prompt seeding.
apps/native/src/components/widget/filesystem/filesystem-step.tsx	Implements onTrackSystemDefaults (direct apply) and refreshes the scan after applying.
apps/native/src/components/widget/filesystem/file-list.tsx	Plumbs the new system-defaults tracking handler through the file list.
apps/native/src/components/widget/filesystem/data.ts	Adds a helper to detect the system-defaults candidate section.
apps/native/src-tauri/src/system/scanner.rs	Adds NULL_FLAG, StringFromIntMap, updated comparison logic, and Nix generation enhancements with tests.

Comments suppressed due to low confidence (1)

apps/native/src-tauri/src/system/scanner.rs:1617

• default_value is sent to the frontend as-is. When the factory default is NULL_FLAG, this leaks the internal sentinel string ("NULL") into UI strings like "default: …" and any previewed Nix snippet metadata. Consider translating the sentinel to something user-facing (e.g. "null") before returning it.

                defaults.push(SystemDefault {
                    nix_key: def.nix_key.to_string(),
                    label: def.label.to_string(),
                    category: def.category.to_string(),
                    current_value: current.to_string(),
                    default_value: def.factory_default.to_string(),
                });