Implement push-based inhibition capabilities

[Staphylococcus]

Parent: #216, within the #89 GNOME/Plasma MVP. Target: v1.8.0.

Outcome

Implement push-based inhibition, starting with GNOME SessionManager. Each capability maintains current inhibition state from ordered source events and exposes a Boolean permission facade, with separate diagnostics. The section combines participating adapters' Booleans.

Scope

• Implement inhibition only, following Compose independent activity and inhibition capabilities for GNOME and Plasma #216's independent capability contract. An adapter may also supply activity, but sharing a source/connection does not merge those paths.
• Establish initial GNOME inhibition state and refresh after reconnect. Change-only notifications and periodic reconciliation trigger an internal state refresh. Those queries update the same contribution; they do not register GNOME again in Implement pull-based inhibition capabilities #223.
• Keep event ordering, owner validation, obsolete-message rejection, connections and retries inside the adapter.
• Combine different adapters' Booleans: any observed inhibition blocks. Startup, absence and source failure contribute no inhibitor. Quiet healthy subscriptions and pending refreshes retain the last observed state; failed reads drop that source's contribution without manufacturing a release.
• Supply bounded diagnostics consistent with the Boolean. Keep transition history needed by inhibition's release policy internal; aggregate delay belongs to Integrate inhibition at the Boolean blanking gate #225.

Acceptance

• GNOME inhibition is testable without its activity capability; inhibitor events never enter the activity stream or inactivity engine.
• Startup with existing inhibition and changes during initial synchronization are covered.
• Tests cover overlapping inhibitors, one ending while another remains, quiet subscriptions, owner loss/replacement, reconnect and delayed old events.
• Internal refresh queries update one contribution, without an independent pull contributor for the same GNOME fact.
• Section tests combine independent adapters' Booleans and matching diagnostics, including neutral startup/absence/failure, retained state during pending refreshes, and periodic reconciliation of missed additions/removals.

Boundary

#221 owns activity. This slice does not add activity queries, reinterpret idle notifications as inhibition, read preferences, implement aggregate release delay or decide TV actions. #223 implements capabilities whose acquisition mode is pull. #225 joins inhibition permission with activity eligibility only at can_blank().

Completion record — 2026-09-12

Implementation merged into dev in #227. The current runtime suite passes (1,019 unit tests, 151 Cucumber scenarios and runtime integration tests), including activity delivery, private-bus inhibition, cancellation/recovery, preference and gate coverage.

Real GNOME SessionManager overlap, final-release delay and gamepad/restore checks passed. Periodic refresh, owner replacement and obsolete events are covered by adapter tests.

#216 retains native Wayland coverage; #217 retains remaining VM lifecycle validation; #218/#219 retain portable configuration and diagnostics work. No prerelease/main promotion is authorized by closing this implementation slice.