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Re-diagnosis of the "btrfs-assistant 2.2 segfaults on launch" bug, and the fix is not the planned nixpkgs override: 1. gdb: the crash is btrfs_util_subvolume_iterator_next() — libbtrfsutil's UNPRIVILEGED subvolume-iteration path in btrfs-progs 6.17.1 (upstream-fixed after 6.17.1, kdave/btrfs-progs 886571653). Symbol versions were checked and match: not ABI/link drift. 2. VM A/B on real btrfs: as root it works (exit 0); as a user it segfaults (139). The pkexec launcher runs it as root — so the GUI path was fine all along, except… 3. …the distro shipped NO polkit authentication agent: every pkexec prompt in the session failed silently. That is the actual root cause of "the GUI doesn't open". Shipped: hyprpolkitagent (Hyprland's Qt agent — the prompt is Stylix-themed) via exec-once in hyprland.nix; `nomarchy-menu snapshot` prefers btrfs-assistant-launcher again, with the nomarchy-snapshots fzf flow kept as fallback (and for SSH); checks.snapshot-gui guards the root path + offscreen GUI event loop on a real btrfs volume so a lock bump can't silently regress it. No btrfs-progs patch: all our flows are root-side; the unprivileged fix arrives with a lock bump. Verified: V0 (flake check) + V2 (snapshot-gui check, executed green) + V1 (HM generation builds; hyprland.conf carries the agent exec-once; generated menu passes bash -n with the launcher wiring). Remaining V3 queued: first on-hardware themed polkit prompt. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
74 lines
4.2 KiB
Markdown
74 lines
4.2 KiB
Markdown
# Memory — durable lessons, learned the hard way
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Curated, not append-only: one line per fact, newest at the top of its
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section; delete entries that stop being true. Details usually live in a
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docs/ROADMAP.md decision record — pointer given as (§ item). Add a fact
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here the moment a debugging session teaches you something a future
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iteration would otherwise rediscover.
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## Testing & VM recipes
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- CI (`.gitea/workflows/check.yml`) is **eval-tier only**: the act_runner
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is a docker container (no systemd, no /dev/kvm). Container gotchas are
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documented in the workflow header (single-user Nix + nixbld users,
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`sandbox=false` for Stylix IFD, Nix pinned 2.31.5 vs lazy-trees, no JS
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actions past node20) — learned over the legacy repo's 57 runs; read
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them before touching the workflow.
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- The git server is **Gitea** (gitea/act_runner via docker-compose), NOT
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Forgejo — workflows are read from `.gitea/workflows/` (or `.github/`),
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never `.forgejo/workflows/` (a whole push cycle was lost to that).
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- Reusable headless VM harness: `checks.*` via runNixOSTest — existing
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examples to crib from: `distro-id` (boots + `switch-to-configuration
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dry-activate`), `hardware-toggles` (kernel cmdline/PAM assertions),
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`battery-charge-limit` (fake Mains adapter via `test_power`, real udev
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uevent, `InvocationID` change proves the restart).
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- Themed-desktop screenshots work headlessly: software-GL Hyprland
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(`LIBGL_ALWAYS_SOFTWARE` on virtio-gpu) + `machine.screenshot()` QMP
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dump — prototyped 2026-06-19, kept as the fallback for theme previews
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(§ Visual theme picker).
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- Hyprland/Ghostty need guest GL (`virtio-vga-gl`, `gl=on`) in
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interactive QEMU or the session won't start; black screen ≈ missing GL
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(docs/TESTING.md § gotchas).
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- No KVM = slow, not broken; don't read slowness as failure.
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## Known-broken / watchlist
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- **btrfs-assistant "segfault" was unprivileged-only** (re-diagnosed
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2026-07-04): libbtrfsutil's unprivileged subvolume iteration crashes on
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btrfs-progs 6.17.1 (upstream-fixed after); **as root it works**, and the
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pkexec launcher runs it as root. The real distro bug was **no polkit
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agent in the session** (every pkexec failed silently) — hyprpolkitagent
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now ships (hyprland.nix exec-once). `checks.snapshot-gui` guards the
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root path. Lesson: before "app X is broken", check WHO it runs as — and
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whether polkit prompts can render at all (§ Snapshot browse/restore).
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- **NixOS release bump is a trap:** the discarded attempt
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(branch deleted 2026-06-22) hit a Hyprland OOM blocker; a redo is a
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deliberate `v2`, never part of routine lock bumps.
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- `theme-state.json` is git-tracked inside an 86 MB flake tree, so every
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state write re-copies the source before eval — the wallpapers-artifact
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split (BACKLOG LATER) is the decided fix (§ Faster switches).
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## Gotchas (cost a debugging session once)
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- Never kill a Wayland session-lock client (hyprlock): its crash
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failsafe drops to a tty instead of unlocking (§ Hibernate
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double-unlock).
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- rofi `element-icon size` is one value = a square cell; `WxH` silently
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collapses and non-square icons letterbox — pre-crop images square at
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build (§ Visual theme picker).
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- WirePlumber 0.5 monitor rules can only early-match `device.api`;
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`device.product.name` etc. bind *after* the rule runs — surgical
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libcamera scoping is impossible (§ Webcam).
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- `hyprctl switchxkblayout` is a *global* layout flip; per-device isolation
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needs `device[<name>]:kb_layout` keywords (§ Keyboard layouts).
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- Waybar's clock captures the timezone at construction — a zone change
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needs SIGUSR2 (watcher in `timezone.nix`) (§ Automatic timezone).
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- Waybar `persistent_workspaces` (underscore) is dead syntax silently
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ignored; the hyphen form is honoured and renders phantom workspaces
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(§ Waybar shows non-existent workspaces).
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- GTK4/libadwaita/Qt6 read light/dark from the portal's
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`org.freedesktop.appearance color-scheme` (dconf), not Stylix polarity
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(§ GTK/Qt ignore the theme's mode).
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- Update order matters downstream: `sys-update` (lock) before
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`home-update`, or desktop changes are silently skipped against the old
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lock (README § 3).
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- grub `loadfont`s every `.pf2` in a theme dir — reuse a bundled DejaVu
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rather than shipping fonts (§ Distro branding).
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