periskopio: Dioxus desktop feature-parity port — phase 3.5 keystone

[forkwright]

Goal

Port periskopio (crates/theatron/desktop) to full feature parity as the Dioxus desktop surface for Harmonia, closing the last unchecked Phase 3.5 criterion (kanon projects/harmonia/ROADMAP.md:39).

Context

• Phase 3.5 plan W4 defines ten sub-waves hm-400..409: six feature areas (library browse, playback, DSP controls, management, queue/downloads, settings) plus MPRIS, tray, notifications, window state, file associations, autostart — then a Nix derivation and gated desktop CI (projects/kanon/projects/harmonia/phases/03.5-canonical-storage-and-desktop/PLAN.md).
• Entry gate theatron desktop: crate does not compile (edition-inheritance + orphaned crate-name ref), is CI-invisible, and docs overclaim parity #620 (compile, CI coverage, doc truthfulness) closed 2026-07-23.
• Current state: pre-alpha stub views; the skene client (crates/theatron/core) is not yet wired to any view.

Locked decisions (operator, 2026-08-11)

• Blitz-native from day one: consume theatron's mekhane (windowing, tray, menus); no wry/webkit2gtk surface, per theatron's locked no-browser-surface doctrine. kanon's chalkeion is the existing mekhane consumer to study.
• Adopt the theatron substrate in order: themelion (theme — replaces the hand-rolled provider in src/theme.rs) → keryx (rebase skene's HTTP/SSE client) → bathron (window state, notifications, atomic config writes) → skeue/gramma (components as views grow) → dokimasia (design-token lint in CI).
• Mirror aletheia/proskenion's proven pattern: standalone excluded workspace with its own lockfile, exact dioxus patch pin (=0.7.9), three-scoped Signal<T> state, dual-SSE client architecture, contract test with an explicit endpoint inventory plus an xvfb smoke test, path-filtered desktop.yml.
• Semantic CSS over design tokens; no vestigial Tailwind config (proskenion's is unused — do not copy it).
• The themelion→aggelmata rename (D-062) lands before theatron adoption to remove the crate-name collision.
• Harmonia stays independently buildable: theatron is consumed by pinned git tag from the public repo; no runtime coupling to other fleet services.

Done-when

• The ROADMAP criterion is checkable: library, playback, DSP, management, and platform integration all live in periskopio on the theatron substrate.
• Contract test and headless smoke test green in a path-filtered desktop CI job.
• docs/desktop/architecture.md describes what IS, with no stub overclaim.

[forkwright]

State checkpoint (weekly usage window): the foundation PR (Blitz-native base via mekhane, theatron themelion adoption, exact dioxus =0.7.9 pin, proskenion workspace pattern) was in early setup on branch feat/periskopio-foundation (worktree preserved at ~/dispatch-wt/harmonia-690; no substantive commits yet). D-062 is merged, so the themelion name collision is cleared. Resume there.