Per-Element Write Sites ✍️

Every Element grouped by which filesystem location it touches. Reverse map of UserDotfile and PlatformPaths: those answer “which Element writes here?” — this one answers “where does this Element write?”.

At-a-Glance Matrix 🗺️

Element	Owns paths?	Writes to disk?	Primary destinations
Mountain	🟢 yes (most)	yes	`~/.fiddee/`, `<app_data_dir>/<bundle>/`, `<temp_dir>/land-*`
Cocoon	🟢 yes (via FiddeeRoot)	yes	`~/.fiddee/extensionStorage`, `~/.fiddee/globalStorage`, `~/.fiddee/logs`, `<temp_dir>/vine_fallback.proto`
Sky	🟡 no (writes via webview)	no (fs)	WKWebView localStorage / IndexedDB (managed by OS at `<webview-storage>/<bundle>/`)
Wind	⚪ build-time only	no (runtime)	`Target/` output; no runtime writes
Output	⚪ build-time only	no (runtime)	`Target/` output; no runtime writes
Air	🟢 yes (separate root!)	yes	`<config_dir>/FIDDEE/`, `<data_local_dir>/FIDDEE/`, cache/staging/backups, update history JSON
SideCar	🟢 yes (DNS override)	yes	`<data_dir>/SideCar/dns_override.txt` (Mist DNS data dir), download cache
Grove	🟡 minimal	yes (configs)	`ConfigurationService` writes via `tokio::fs::write`; IPCTransport socket via `temp_dir`
Maintain	⚪ build-time only	no (runtime)	Bash-script edits during build; no runtime writes
Vine	⚪ no	no	Proto files shipped; no runtime writes
Mist	⚪ no	no	DNS / WebSocket; no fs writes
Common	⚪ no	no	Abstract crate; no fs writes
Echo	⚪ no	no	Scheduler; no fs writes
Worker	⚪ no	no	Service Worker; no fs writes
Rest	⚪ no	no	OXC bindings; no fs writes

Mountain ⛰️

The largest write-site domain. Rust backend that owns the ~/.fiddee/ atom, the workbench userdata seeder, the session log, the memento persistence layer, and the VSIX extraction pipeline.

Producer	Writes	Trigger
`Binary/Main/AppLifecycle.rs::Dirs`	All `<app_data_dir>/<bundle>/User/*` seed dirs, default JSON files, `~/.claude/agents`, `~/.copilot/agents`	First boot + every subsequent boot (idempotent)
`IPC/WindServiceHandlers/Utilities/UserdataDir/Ensure.rs`	Same seed set as a fallback (idempotent with `AppLifecycle::Dirs`)	First access to `<app_data_dir>` post-boot
`ProcessManagement/InitializationData.rs::get_or_generate_machine_id`	`<app_data_dir>/<bundle>/machine-id.txt` (UUID)	First boot only; persisted thereafter
`IPC/DevLog/WriteToFile.rs`	`<app_data_dir>/<bundle>/logs/<ts>/Mountain.dev.log` or `<temp_dir>/land-editor-logs/<ts>/` fallback	Every dev-log emission when `Record=1`
`IPC/WindServiceHandlers/Utilities/RecentlyOpened.rs::Mutate`	`~/.fiddee/workspaces/RecentlyOpened.json`	Workspace folder add
`ApplicationState/State/WorkspaceState/WorkspaceDelta.rs::PersistRecentlyOpened`	Same `RecentlyOpened.json`	Workspace delta event
`ApplicationState/Internal/Persistence/MementoSaver.rs`	`<app_data_dir>/<bundle>/...memento.json` (global memento)	Memento update via `storage:set` IPC
`MementoLoader/AttemptMementoRecovery.rs`	`<memento>.json.backup` corruption-recovery sibling	JSON deserialise failure
`MementoLoader/CreateCorruptedBackup.rs`	`<memento>.json.corrupted.<YYYYMMDD_HHMMSS>` timestamped corruption snapshot	JSON deserialise failure (parallel side-channel)
`RunTime/Shutdown/SaveApplicationState.rs`	Final global memento JSON flush	App shutdown
`Environment/StorageProvider.rs`	`<app_data_dir>/<bundle>/User/globalStorage/<extId>/state.json` per extension	Extension `Memento.update()`
`Environment/ConfigurationProvider/UpdateValue.rs` + `Loading.rs`	`<app_config_dir>/User/settings.json`	User settings write
`Environment/KeybindingProvider.rs`	`<app_config_dir>/User/keybindings.json`	Keybinding edit
`Environment/Terminal/ShellIntegration.rs`	`<temp_dir>/land-zsh-integration-<pid>/.zshrc`	Integrated-terminal launch
`Environment/WorkspaceProvider.rs`	`<workspace>/<tempfile>` (atomic write-rename)	Workspace file save
`Environment/FileSystemProvider/WriteOperations.rs`	Arbitrary user-workspace paths (Cocoon→Mountain write_file IPC target)	Extension file write
`ExtensionManagement/VsixInstaller.rs`	`~/.fiddee/extensions/<id>/...` (VSIX extraction + `HealExecutableBits`)	VSIX install
`RPC/CocoonService/FileSystem/*`	Arbitrary user-workspace paths (gRPC file-system service surface)	Cocoon gRPC `write_file` / `create_directory` / `rename_file` / `copy_file`
`Maintain/Build/Manifest/PreBake.ts` (build-time, not runtime)	`Element/Mountain/Target/<profile>/extensions.manifest.json` (pre-baked extension list)	`beforeBundleCommand` in `tauri.conf.json`; accelerates boot-time scan to <50 ms

Cocoon 🦋

Node.js extension host. Writes per-extension storage roots under ~/.fiddee/ and a temp proto when the bundled proto resource is missing.

Producer	Writes	Trigger
`Services/Handler/Extension/Host/ActivateExtension.ts:51-53`	`~/.fiddee/extensionStorage/<extId>/`, `~/.fiddee/globalStorage/<extId>/`, `~/.fiddee/logs/<extId>/`	Extension activation
`Services/Extension/Context.ts:495-496`	`~/.fiddee/extensions/<id>/.storage/` (in-bundle), `~/.fiddee/globalStorage/<extId>/`	First call to `context.globalState` or `context.workspaceState`
`Services/Mountain/Client/Service.ts:558`	`<temp_dir>/vine_fallback.proto`	gRPC client init when bundled proto resource is missing
`Services/gRPC/Server/Service.ts:1664`	Same `<temp_dir>/vine_fallback.proto` (parallel fallback)	gRPC server init when bundled proto resource is missing
`Platform/FiddeeRoot.ts`	(resolver only, no write)	TypeScript mirror of Rust `FiddeeRoot.rs`

Cocoon never writes to <app_data_dir>/<bundle>/ directly — all per-bundle writes are proxied through Mountain via IPC (storage:set, secrets:set, file-system gRPC).

Sky 🌌

Sky writes via the OS-native webview storage APIs; the actual filesystem destination is the webview’s per-bundle storage tree (~/Library/WebKit/<bundle>/ on macOS, ~/.local/share/<bundle>/ on Linux, %LOCALAPPDATA%\\<bundle>\\EBWebView\\ on Windows).

Producer	localStorage key	Purpose
`Workbench/Bundled/Electron/Entry.ts`, `Sky/Bridge.ts`	`Disable`	UI-fix toggle. Survives reload.
`Sky/Function/SmokeTest/Auto/Diagnose/Input.ts`	`Disable`	Smoke-test side reads the same key.
`Sky/Function/SmokeTest/Run/Command/Catalog/Smoke/Test.ts`	`Smoke`	Sticky smoke-test gate.
`Workbench/Electron/Post/Hog/Bridge.ts`	PostHog distinctId	Per-install PostHog telemetry identifier. Separate from Mountain’s `machine-id.txt`.
Workbench-internal (VS Code `LocalStorageService`)	(many)	Editor state, layout, opened editors, … Not enumerable from source without runtime inspection.

Sky does not make direct filesystem writes. Every “write” goes through the webview’s storage layer or via MountainIPCInvoke IPC to Mountain (which then writes the file).

Wind 🍃

Build-time only. Reads process.env and import.meta.env to compose the ESBuild config and PostHog telemetry constants. No runtime filesystem writes.

Producer	Reads (build-time)	Purpose
`Source/ESBuild.ts`	`Clean`, `Meta`, `NODE_ENV`, `TAURI_ENV_DEBUG`	Bundle build configuration.
`Source/Telemetry/PostHog/Configuration.ts`	`import.meta.env` + `process.env` fallback for PostHog config	Telemetry constants baked into the bundle.
`Source/Configuration/ESBuild/Config/TargetConfig.ts`	`Authorize`, `Beam`, `Capture`, `Report`, `Brand`, `Buffer`, `Batch`, `Throttle`, `Cap`	esbuild `define` keys; substitute literals at build time.

Output ⚫

Build-time only. Same shape as Wind — reads env, no runtime writes.

Producer	Reads (build-time)	Purpose
`Source/ESBuild.ts`	`Browser`, `Electron`, `Clean`, `Dependency`, `Level`, `Meta`, `NODE_ENV`, `TAURI_ENV_DEBUG`	Output bundle build configuration.
`Source/ESBuild/Output.js`	`Compiler`, plus the full PostHog set	Compiler dispatch + PostHog `define` block.
`Source/ESBuild/Rest/Plugin.ts`	imports `tmpdir` from `node:os`	Compiler-temp directory at build time (not runtime).

Air 💨

Background daemon. Uses a different filesystem root than Mountain — <config_dir>/FIDDEE/ (uppercase) and <data_local_dir>/FIDDEE/, not ~/.fiddee/ (lowercase). Reconciliation candidate — see Encapsulation §H for details.

Producer	Writes	Notes
`Source/Updates/mod.rs:1668-1694`	`<config_dir>/FIDDEE/`, `~/.config/land/`, `<data_local_dir>/FIDDEE/`, `~/.local/share/land/`	Update backup destinations (multiple candidates probed).
`Source/Updates/mod.rs:450-464`	`<cache>/staging/`, `<cache>/backups/`	Staging + rollback directories under the configured cache.
`Source/Updates/mod.rs:1277`	`<updates>/history.json`	Update history JSON.
`Source/Downloader/mod.rs:448, 578, 2140`	`<cache>/` + `<destination>.chunks/chunk_NNNN`	Download cache + per-chunk temp files.
`Source/Authentication/mod.rs:326-330`	`<credentials-store-path>` (resolved at config time)	Credentials store (separate from OS keychain).
`Source/Binary/Binary.rs:1770`	Arbitrary `path` argument from caller	Binary copy / install.
`Source/Initialize/Configure/Log/ConfigureLog.rs`	`AIR_LOG_FILE` env-controlled destination	Daemon log file.
`Source/Initialize/Command/HandleCommand.rs:393`	`AIR_LOG_DIR` env-controlled destination	Daemon log directory.

<config_dir> and <data_local_dir> resolve per-OS via dirs::config_dir() / dirs::data_local_dir() (see PlatformPaths for the resolution table).

Air is the only Element today that uses SCREAMING*SNAKE_CASE env vars (AIR_LOG*) — the project convention permits it for the daemon because Air ships as an external tool with its own naming convention.

SideCar 🛟

Producer	Writes	Trigger
`Source/Spawn.rs:56-61`	`<data_dir>/<override_path>` (`DNS_OVERRIDE`)	First Mist DNS configure
`Source/Source/SideCar/Spawn.rs:48-53`	Same (mirrored handler)	Same trigger
`Source/Download.rs:165, 555, 628`	`<CachePath>`, `<Parent>`, `<TempDownloadsDirectory>/`	SideCar package download

SideCar paths are resolved via the parent SideCar process’s CLI args; not under FiddeeRoot.

Grove 🌳

Producer	Writes	Trigger
`Source/Services/ConfigurationService.rs:194`	`<path>` (arg-controlled)	`ConfigurationService.write()` API
`Source/Transport/IPCTransport.rs:96`	`<temp_dir>/<socket>` (Unix socket path)	IPC transport bind
`Source/DevLog.rs:54`	(env read; no write)	Dev-log home resolution
`Source/API/VSCode.rs:723, 738`	(env read; no write)	`vscode.env.machineId` / `VSCODE_APP_ROOT` proxy

Maintain 💪🏻

Build-time only. Reads env (get_env, env, vars) and runs Rhai scripts. No runtime writes; build-time writes are to Target/ and to temporarily rewritten manifest files (Cargo.toml.Backup residue is the known leakage — see PlatformPaths §In-tree build artefacts).

Elements With No Filesystem Writes ⚫

For completeness:

Element	Role	Notes
Common	Abstract crate (traits, DTOs, `ActionEffect`)	Foundational; no concrete I/O.
Echo	Scheduler runtime	No filesystem; manages tokio tasks.
Mist	DNS + WebSocket transport	Network-only.
Rest	OXC / Rust language bindings	Build-time dependency surface.
Vine	gRPC proto + transport (planned crate split)	Proto resource lookup only.
Worker	Service Worker bundle	Webview-only; no Node fs access.

Filesystem Footprint — Per-Element Write Sites