# Gotchas — landmines this codebase has already stepped on

Every one of these caused a real bug or debugging spiral. Read before
touching the adjacent code.

## Angular (v22, zoneless, signals, OnPush)

- **Never consume push streams through signal+effect.** An effect that reads
  a signal and (directly or transitively) writes signals re-triggers itself —
  this froze the entire app on the first transfer. Push messages
  (transferUpdate etc.) go through plain callback registries in RpcService.
  Signal coalescing would also silently drop intermediate progress snapshots.
- **No signal writes during template render** (NG0600). Anything that loads
  panels from code paths reachable during render defers with
  `queueMicrotask` (see `PanelsService.newWorkspace`).
- **`[value]` on `<select>` is applied before `@for` options render** and
  silently selects nothing. Use per-option `[selected]` bindings (connection
  manager stack picker).
- Template bindings with special characters: `[class.bg-primary/15]` works;
  `[class.shadow-[...]]` (brackets) does NOT parse — use `[style.box-shadow]`.
  Static class attributes may use arbitrary values freely.
- Functions called from templates ARE reactive: signals read inside them
  register on the view's consumer (call-stack-based tracking). That's why a
  template calling `i18n.t()` re-renders on a language switch — `t()` reads
  the `locale` signal.
- Dedicated tools > shell: IDE diagnostics between paired template/class
  edits are often stale mid-sequence — trust `bun run build:ui` (full AOT
  type-check), not the first red squiggle.
- Tailwind v4 canonical class names: `wrap-break-word` not `break-words`,
  `accent-primary` not `accent-[var(--primary)]`, `z-60` not `z-[60]`.
  Every color used in a template must resolve through `@theme inline`.
- Stylesheet `url()` must resolve at BUILD time: assets referenced from
  `styles.css` live under `ui/src/` (esbuild emits them hashed into `media/`
  and rewrites the url), NOT `ui/public/` — a public path fails the build with
  "Could not resolve".
- **Two `class` attributes on one element: the second is silently dropped.**
  No warning, no build error — the layout classes simply never apply. This
  collapsed the tab strip and two window headers at once (`fe028a9`), because
  a scripted edit appended `class="…"` to elements that already had one.
  When removing a conditional binding, check what the branch *contained*: the
  bindings there were genuinely dead, but the layout classes inside them were
  not, and nothing replaced them.
- **A component `template:` is a TS template literal, so no backticks inside
  it** — not even in an HTML comment. A backtick in a comment terminates the
  literal and the errors point at the prose, not at the quoting.
- **Reach `core/` through the `@core/*` alias, never a relative path.**
  Components sit at varying depths and get moved; the alias is what let 67
  imports survive two relocations untouched. A `../../core/...` path is a
  future merge conflict.
- **The build DOES type-check components nothing imports.** ngtsc compiles the
  whole program, so an unreferenced component still fails `bun run build:ui` on
  a type or template error (verified by injecting an error into an
  unreferenced file).
- **`overflow-x: auto` also clips vertically.** CSS refuses to pair `visible`
  with a non-visible axis, so the computed `overflow-y` becomes `auto` too:
  anything poking out of a horizontally scrolling strip (a raised tab, an
  underline at `-bottom-px`) is silently clipped. Reserve padding instead.

## Theming (`ui/src/styles.css`)

- **A new surface token needs an AMOLED line, or AMOLED stops being
  all-black.** The two `[data-dark-tone='darker']` blocks re-declare every
  surface (`--chrome`, `--toolbar`, `--background`, `--row-alt`, …) as `#000`;
  a token added only to the dark blocks shows through in AMOLED. Tokens derived
  in `:root` by `color-mix` (`--toolbar-2/-3`) follow on their own.
- **Hover/selected color is a translucent overlay (`--accent`).** An opaque
  hover vanishes on a surface of its own lightness — light's old 0.967 hover
  on the 0.965 header strip did exactly that. Keep `--accent` alpha-based when
  retoning surfaces.
- **A native control ignores `border-radius` and background until
  `appearance: none`.** WebKit draws checkboxes, radios and selects itself;
  the square restyle in the `@layer base` block depends on it. Put `pl-*`,
  never `px-*`, on a `<select>`: utilities outrank the base layer, so a `px`
  utility would erase the padding-right the drawn caret lives in.
- **A custom `::-webkit-scrollbar` turns off macOS overlay scrollbars.** The
  moment the pseudo-element is styled, WKWebView draws classic always-visible
  scrollbars that take layout width. Deliberate here (square design); don't
  reach for it to "tint" scrollbars without accepting that.

## The interface scale (root font-size lever)

- **electrobun's native page zoom is a silent no-op on Linux — do not reach for
  it.** `webviewSetPageZoom` in the shipped `libNativeWrapper.so` (v1.18.1, and
  the `_cef.so`, and the copy in our own build output) is a compiled
  empty-body stub: the disassembly has no `call` instruction, and
  `webkit_web_view_set_zoom_level` is not even in the library's imports.
  `webviewGetPageZoom` returns a hardcoded `1.0` from `.rodata`, so the failure
  is unobservable through the API — set 2.0, read back "1.0 = success". The
  JSDoc's "(WebKit only)" means macOS WKWebView. This is why the scale is CSS.
- **Everything the UI sizes with must be rem.** The scale works by setting the
  root font-size, so a px value freezes while everything around it grows. The
  px reservoirs were the panel-chrome tokens (`--row-h` etc.) and 93
  `text-[11px]` arbitraries. 1px hairlines and focus rects stay px deliberately
  (crisp at any scale).
- **px constants in TS that mirror rem-sized CSS are latent scale bugs.** The
  context menu's `MENU_W = 224` was a hardcoded mirror of `w-56`
  (14rem): box grew, math didn't, flip fired at the wrong edge. Convert through
  `@core/metrics` `remPx()` at use time — it reads the LIVE root font-size,
  and per call, since the scale changes mid-session. The editor's canvas-based
  `charWidth` is cached keyed on the computed font string for the same reason.

## Electrobun

- **The prebuilt CLI binary ships with a broken ad-hoc signature**, so macOS
  SIGKILLs it at exec and `bun run start` prints nothing and exits **0** —
  `bin/electrobun.cjs` spawns the real binary and forwards
  `process.exit(code || 0)`, and a signal death has `code === null`. The binary
  is a Bun single-file executable whose payload is appended *after* the linker
  signed it, so `codesign -v` reports "code or signature have been modified";
  the arm64 and x64 CLI tarballs are both affected upstream (confirmed by
  hashing a fresh download against the shipped copy — it is not local
  corruption, and re-installing does not help). `scripts/fix-electrobun-cli.ts`
  re-seals it with `codesign --force --sign -`. It runs from `postinstall`
  **and** ahead of every electrobun invocation, because the wrapper downloads
  the binary **lazily on first use**, not at install time — postinstall alone
  would no-op on a fresh checkout. It also fixes `.cache/electrobun`, which the
  wrapper restores `bin/` from. Never read a silent `exit 0` from the
  electrobun CLI as "nothing happened": run `codesign -v` on it first.
- **Window `close` is not cancellable** (response type `{}`; only the
  app-level `before-quit` supports `event.response = {allow:false}`). All
  unsaved-state guards must either intercept app-controlled close paths
  (⌘W, buttons) or survive the close (editor draft mirroring).
- **⌘W in any secondary window arrives as the MAIN window's `close-tab`
  menu action** (macOS: the app menu intercepts it before the webview sees
  the key). bun must check the focused secondary window first — the Settings
  window, then editors — and close THAT; a new window kind that skips this
  check makes ⌘W close a main-window tab behind it.
- **One rpc instance per window** — BrowserView binding steals the rpc's
  transport; a shared instance silently sends to the wrong webview.
- **RPC before socket open is silently lost.** Everything gates on the
  socket-open promise (RpcService `ready`).
- The emitter has no `off()`. Window event closures must not capture records
  you want garbage collected.
- `electrobun build` defaults to the **dev** channel; release builds need
  `--env=stable`. The stable app name differs from the dev one
  (`miniSCP` vs `miniSCP-dev`), including the app-data dir implications when
  testing.
- Tray: never call `setImage` after construction on macOS — the template
  treatment is lost and the icon renders black on dark menu bars.
- `ApplicationMenu` is macOS-only in our usage; accelerators on Windows are
  single-character only.
- **`ContextMenu.showContextMenu` is a silent no-op on Linux** (electrobun's own
  `dist/api/bun/proc/linux.md` says so; the app also prints "Application menus are
  not supported on Linux" at boot). Because the UI suppresses the webview's own
  right-click menu, that left EVERY panel context menu dead on Linux — no error,
  nothing happens. The menu is plain HTML now (`ui/src/app/skins/shadlike/context-menu.ts`) on
  every platform; don't reintroduce the native one for "nativeness" on mac/win
  without keeping a Linux path.
- **Window-open flash prevention is three-layer** — remove any one and the
  white/inverted blink returns: (1) windows are created `hidden: true` and
  revealed by `showWhenReady` on the webview's first `dom-ready` (800 ms
  fallback), (2) the bun preload bakes the persisted `data-theme`/tone
  attributes and the interface scale before first paint (`buildPreload`),
  (3) `ui/src/index.html` carries an inline `<style>` with the html background
  per theme — its oklch values MUST stay in sync with the `--background` tokens
  in styles.css. (The win7 branch once replaced (3) with a transparent rule and
  the modern skin silently lost it — the other two layers do not cover it.)
- Dev vs prod URL: `getMainViewUrl()` resolves the ng-serve dev server only
  when `DEV_SERVER_URL` is set AND the updater channel is `dev` AND the
  server answers a HEAD request; secondary windows must reuse the resolved
  URL, never hardcode `views://`.
- Upstream Bun panic (`FFI_Callback_threadsafe_call` → `web_worker.spin`):
  rare segfault under long sessions; upstream electrobun×Bun issue, restart
  recovers, nothing app-side to fix.
- **Preloads and frames are construction-time only.** The preload is a
  persistent `WebKitUserScript` at DOCUMENT_START, frozen at webview
  construction — `webview.loadURL()` re-runs the OLD one
  (`updatePreloadScriptToWebView` is only reachable from electrobun's internal
  `<electrobun-webview>` handler). `titleBarStyle`/`transparent` have no
  setters. Anything `buildPreload` bakes is a first-paint snapshot the UI must
  correct live over RPC. Recreating the main window is not an escape hatch:
  `exitOnLastWindowClosed`, push closures and the tray capture it, and there
  is no `off()`.
- **Drag regions ignore `preventDefault`.** The preload starts a window move
  from a bubble-phase `mousedown` on `document` and never reads
  `defaultPrevented`; a `pointerdown` handler doesn't stop it either (the
  compat `mousedown` still fires). `isAppRegionDrag` checks
  `.electrobun-webkit-app-region-no-drag` first — that class on the element is
  the only reliable suppressor (`dist/api/bun/preload/dragRegions.ts`).
- **No resize, maximize-event or double-click-maximize primitives (1.18.1).**
  `titleBarStyle: "hidden"` drops the whole frame (Cocoa `Titled` — the only
  way to remove the traffic lights; `gtk_window_set_decorated(false)` on
  Linux) and with it the WM resize borders; nothing restores them (no
  `startWindowResize`, no `gtk_window_begin_resize_drag`, no
  `setResizable`/min-size options — only `setFrame`/`getFrame`). No maximize
  event exists (derive it from `resize` + `isMaximized()`), and drag regions
  don't double-click-maximize. A custom-chrome window has to build all three.

## Linux

- **`ERR_DLOPEN_FAILED` on `bun run start`** means a missing system library, not
  broken app code. `libNativeWrapper.so` links `libayatana-appindicator3.so.1`
  *hard* (for the tray), so the app cannot start at all without it — even though
  the tray is a minor feature. Diagnose with
  `ldd build/dev-linux-x64/*/bin/libNativeWrapper.so | grep 'not found'`; the
  `libasar.so => not found` line in that output is a red herring (it ships beside
  the wrapper and resolves at load). Install list per distro is in
  [platform-notes.md](platform-notes.md).
- **Black window on NVIDIA + `Failed to create GBM buffer of size WxH: Invalid
  argument`** (usually with `X11 Error: GLXBadWindow (code 170)`). The app boots,
  logs "miniSCP started", reports no error — and paints nothing. WebKitGTK's
  DMABUF renderer can't allocate buffers on the NVIDIA proprietary driver;
  `WEBKIT_DISABLE_DMABUF_RENDERER=1` is the upstream workaround.
  - **The app cannot apply this to itself.** WebKit reads the variable when it
    forks its web process, and **Bun's `process.env` writes do not propagate to
    child processes** (verified: a spawned child sees it unset). Setting it in
    `src/bun/index.ts` — even in a module imported before `electrobun/bun` —
    does nothing. It must be in the environment before the app process starts.
  - Hence every launch path injects it: `scripts/linux-gpu.ts` (`launchEnv()`)
    for `bun run dev` / `bun run start`, and the `miniSCP.sh` wrapper that
    `release.ts` writes beside `bin/launcher` in the tarball. **A new launch
    path must call `launchEnv()` or it will render black on NVIDIA.**
  - Gated on `/proc/driver/nvidia` so Intel/AMD keep hardware compositing, and
    an explicit `WEBKIT_DISABLE_DMABUF_RENDERER` from the user always wins.
  - A "does it boot?" log check does NOT catch this — grep for the GBM line, or
    look at the window.
- **`bun run start` leaves the old instance running, and
  `import -window miniSCP` grabs the OLDEST match.** Instances pile up across
  rebuilds, so every screenshot silently comes from a stale build and the fix
  you just made looks like it did nothing. Cost three wrong readings in one
  session, including a "the CSS is in the bundle but does not apply" dead end.
  Kill first (`pkill -f dev-linux-x64`), confirm with
  `pgrep -cf 'dev-linux-x64/miniSCP-dev/bin/launcher'`, then launch and capture.
  Note `pkill -f 'electrobun dev'` also matches the shell running it and kills
  your own command (exit 144) — match on the build path instead. That is only
  half the trap: `pkill -f dev-linux-x64` does the same thing, because the
  pattern appears in the killing command's OWN argv. Break the literal with a
  character class — `pkill -f 'dev-linux-x[6]4'` — the way `ps | grep [x]yz`
  has always worked.
- **Launching the app steals focus — ask first.** `bun run start` opens a real
  window that takes focus, which interrupts whatever the user is doing; there
  is no Xvfb/xvfb-run on this machine and Wayland offers no
  launch-without-focus. Batch every live check into a single launch.
- Benign startup noise on Linux — non-fatal, the app runs normally:
  `libayatana-appindicator is deprecated. Please use libayatana-appindicator-glib`
  (upstream electrobun's choice, not ours).

## Domain logic

- **sessionId ≠ filesystem identity.** Two panels on the same server are two
  SSH sessions. Every same-file/nested-path guard compares `fsKey`
  (`resolvedIP:port` / `"local"`); comparing sessionId caused a
  truncate-to-zero data-loss bug. When fsKeys differ but paths collide, the
  probe-file check unmasks aliased hosts. Never "simplify" this back.
- `createWriteStream` truncates BEFORE the source is read — that's why
  self-copy is destructive, and why guards must run before any stream opens.
- The synthetic `'..'` row: type `'dir'`, must be excluded from selection,
  targets(), filtering match-count, kind/rights/owner display, and drag
  sources. Any new row-level feature must decide what `'..'` does.
- `Semaphore.wake()` must reserve slots synchronously; waking waiters that
  increment asynchronously loses budget under concurrent release.
- Settings: the backend spread-merges (`{...DEFAULT_SETTINGS, ...data}`) so
  new keys auto-default, but the UI SettingsService reads field-by-field —
  a new setting silently stays at default until wired in all five spots.
- **Every window's RPC must serve `saveSettings`.** The scale shortcuts
  shipped in editor and manager windows while only the main RPC served it:
  the request went unanswered, the change applied locally, and main's next
  broadcast snapped it back. All three factories now share
  `saveSettingsHandler`, and `settingsSaved()` in index.ts rebroadcasts to
  every window but the sender — an echo would drag a held Cmd+ backwards.
- The editor draft mirror sends full content per tick (2 MB cap upstream);
  don't shrink the 400 ms debounce.
- `panel.touched` gates localDir auto-navigation; `connectToken` guards
  against a slow connect resolving into a panel the user already reused.

## i18n

- **Translations live in `src/shared/i18n/*.ts` (TS, not JSON)** — deliberate:
  it sidesteps `resolveJsonModule` differences between the Angular esbuild and
  Bun builds and gives full typing. `en.ts` is the source of truth; other
  locales are partial and fall back to English then the raw key.
- **`i18n.t()` is reactive because it reads the `locale` signal** — that's what
  makes live language switching work with no pipe. If you cache a translated
  string in a plain field it WON'T update on switch; call `t()` in the template
  (or in a signal-reading getter) instead. Same for `i18n.date()/size()`.
- Dictionary values are TS string literals: **French/other apostrophes break
  single-quoted entries** (`'…c'est…'`). Use double quotes for any value
  containing an apostrophe. Plurals are `{ one, other }` maps (not ICU strings);
  zh/ja supply only `other`.
- **Native menus can't use the Angular service** — `menu.ts` goes through backend
  `i18n.ts`, and the app menu must be rebuilt when the locale changes (wired in
  index.ts `settingsChanged`), or it keeps the old language. The context menu no
  longer has this problem: it is Angular now and reads `I18nService` directly.
- `eu`/`zh`/`ja` are AI drafts pending native review (see the i18n README).
- **Silent auto-refresh must snapshot sessionId+cwd and discard a mismatched
  result.** A normal `refresh()` is masked by `busy` (input blocked), but the
  silent variant (poll/watch) runs while the user can navigate — without the
  guard, a poll that started in dir A resolves and stamps A's listing over the
  dir B the user just opened. It also never calls `scrollCursorIntoView`
  (scroll must stay put) and returns early if `busy()` or already refreshing.

## Build / tooling

- Angular CLI rejects Bun's Node-compat version — `scripts/node-version-shim.ts`
  is preloaded via `bunfig.toml` at the root AND in `ui/`. Removing either
  breaks `ng`.
- ssh2's optional native deps must stay `external: ["cpu-features", "*.node"]`
  in `electrobun.config.ts` — bundling them breaks the build; ssh2 falls back
  to pure JS at runtime.
- `bun run --cwd ui build` (flag order matters; `bun --cwd ui run build` does
  not do what you want).
- `version.gen.ts` is gitignored and regenerated by postinstall + every build
  script; a fresh checkout fails `tsc` until `bun install` (or any script)
  has run once. Never commit it — it would bump the commit count it records.
- Icon pipeline is `scripts/gen-icons.ts` (resvg) — regenerate after touching
  `assets/logo.svg` or `assets/tray/tray-glyph.svg`; the .ico and tray PNGs
  are build inputs, not build outputs.