Build native adaptive terminal workspaces

[msitarzewski]

Summary

• Replace the former AppKit tab-group mirror with model-owned adaptive terminal sessions and native sidebar presentation.
• Give Connections and terminal windows consistent full-height native sidebars, unified compact titlebars, stable tool clusters, and responsive narrow-window behavior.
• Preserve the shared one-target architecture across macOS, visionOS, iPadOS, and iOS while keeping Mac window policy inside the existing platform boundary.
• Expand workspace/session restoration, movement, local/SSH parity, interaction coverage, and release documentation.
• Update the codex-completions Memory Bank phases 06/07 with the approved architecture and current evidence.

Why

The old tab-mirroring and duplicate chrome paths created competing navigation ownership, toolbar movement, inconsistent sidebar material, and fragile AppKit observation. The revised design keeps session identity and lifetime in the existing workspace/session models, lets SwiftUI/AppKit own their native presentation responsibilities, and removes redundant custom surfaces.

Product invariant

The terminal canvas remains independently tintable, translucent, blurred, or fully transparent. Glyphs and cursor stay above that composition. Shared session, appearance, trust, and credential authorities continue to serve every supported Apple platform.

Validation

• macOS 27 / Apple Silicon unit tests: 274 passed, 0 failed, 0 skipped, 0 runtime warnings
• visionOS 27 simulator build: passed
• iPadOS 27 simulator build: passed
• iOS 27 simulator build: passed
• staged git diff check: clean
• production TODO/FIXME/incomplete-marker scan: clean
• staged Gitleaks scan: clean
• user visual validation: approved for Connections and terminal chrome, sidebar ownership, local/SSH parity, compact tool groups, and narrow-window behavior

Explicit evidence boundary

The full macOS UI harness was stopped after its host runner stalled between app launches. Its run is not represented as passing; bounded unit coverage, target builds, static checks, and user visual validation are the publication evidence for this checkpoint.

Impact radius

Shared model/session changes are covered by shared tests and cross-platform builds. macOS-only window policy and toolbar behavior remain under Platforms/macOS; visionOS/iPadOS/iOS retain their native presentation paths and the shared terminal rendering/appearance authority.