refactor: unify window portal registries behind one hosted-view base

[arzafran]

What this does

Removes the line-for-line duplication between the two window-level portal registries — WindowTerminalPortal (hosts terminal surfaces) and WindowBrowserPortal (hosts browser web views) — by pulling out the parts of their lifecycle that are genuinely identical into a new shared base class. This is nuclear-review finding N4/WP3, called out as the highest-risk item in the audit, so the goal here was provable correctness over maximal dedup: only code that is byte-identical (or identical modulo a per-class debug-log line) moved into the shared base; everything with real behavioral differences was left alone, even where it shares a name.

Summary

New file Sources/HostedViewPortalRegistry.swift (@mainactor class, +147 lines) holds:

• Shared bookkeeping: window, installedContainerView, installedReferenceView, geometryObservers
• removeGeometryObservers()
• effectiveAnchorFrameInWindow(for:)
• synchronizeHostFrameToReference() — per-class dlog preserved verbatim via an overridable logHostFrameUpdate(_:) hook
• debugHostedSubviewCount()
• Static geometry helpers: rectApproximatelyEqual, pixelSnappedRect, isHiddenOrAncestorHidden, isView(_:above:in:)

WindowTerminalPortal and WindowBrowserPortal now subclass HostedViewPortalRegistry and override hostViewForGeometry to expose their concrete host view (WindowTerminalHostView / WindowBrowserHostView, both unmodified) to the shared geometry code.

Line deltas:

File	Before	After	Delta
Sources/TerminalWindowPortal.swift	2148	2045	-103
Sources/BrowserWindowPortal.swift	4177	4075	-102
Sources/HostedViewPortalRegistry.swift	—	147	+147

Kept-divergent methods (compared method-by-method, left alone deliberately)

Method	Why it stays split
pruneDeadEntries	Terminal prunes non-visible entries once their anchor is dead; browser deliberately keeps them so a hidden WKWebView can be rebound on workspace switch without a full reload. Opposite pruning policy, not incidental.
resetTransientRecoveryRetryIfNeeded / scheduleTransientRecoveryRetryIfNeeded	Terminal's retry budget is gated behind PROGRAMA_ISSUE_483_PORTAL_RECOVERY and resets only when exhausted. Browser's is always enabled and resets whenever the recovery reason changes (tracked per-entry, extra Entry.transientRecoveryReason field). Different coalescing semantics — explicitly called out as must-not-touch.
installGeometryObservers(for:) / ensureInstalled()	Terminal uses Auto Layout constraints and orders itself below the last WindowBrowserHostView; browser is frame-based and orders itself above the last WindowTerminalHostView/reference. This pair is the actual z-order coordination contract between the two portal types.
bind / detachHostedView↔detachWebView / hideEntry↔hideWebView / updateEntryVisibility / synchronizeHostedView↔synchronizeWebView	Browser wraps each WKWebView in a WindowBrowserSlotView container (drop-zone overlay, search overlay, hosted-inspector-divider, WebKit lifecycle notifications); terminal parents the hosted view directly into the host. Two-level vs one-level containment — not safely generalizable without touching WebKit-specific and terminal-specific code.
tearDown()	Terminal additionally deactivates/clears Auto Layout constraints (2-line diff). Left as two small separate implementations rather than adding an abstract-method hook for a trivial difference.
scheduleDeferredFullSynchronizeAll() / debugEntryCount()	Same shape but reference different backing dictionaries, and the schedule method has asymmetric debug logging (terminal has none, browser logs entry counts). Left as near-duplicate one-liners rather than adding indirection for marginal benefit.

Off-limits, untouched

• WindowTerminalHostView and its hitTest() (typing-latency-sensitive path per repo CLAUDE.md) — not modified at all.
• WindowBrowserHostView — not modified at all.
• All WebKit-specific recovery, drop-zone/search-overlay/hosted-inspector-divider logic, and all terminal-specific attach/refresh logic — untouched, stayed in the adapters.
• Geometry-sync coalescing semantics (generation counters, live-resize immediate paths, double-async settle delay) — unchanged on both sides.

Xcode project

Registered Sources/HostedViewPortalRegistry.swift in project.pbxproj with the standard 4 entries (PBXBuildFile, PBXFileReference, group child, Sources build phase), IDs A5FF0008/A5FF0018 — verified no collision with existing IDs.

Test Plan

• xcodebuild -scheme programa -configuration Debug build → ** BUILD SUCCEEDED **
• xcodebuild -scheme programa-unit build-for-testing → ** TEST BUILD SUCCEEDED **
• CI: ui-regressions and tests-build-and-lag workflows are the real arbiters here, not the local build — this touches the terminal/browser portal geometry-sync and z-ordering paths on every window resize, split-divider drag, and pane bind/detach. Please wait for both to go green before merging.
• Not done (per repo policy): did not launch the app locally, did not run tests locally.