sessions: Redesign session list with hover-reveal show-more, PR status icons, and compact layout

[osortega]

Summary

Redesigns the agent sessions list in the sessions app to match the prototype mockup. All changes are scoped to the sessions app layer — the core workbench session list is unaffected.

Changes

Show-more/show-less with hover animation

• Show-more rows start collapsed at 1px height (effectively hidden)
• Hovering any card in a section reveals the show-more with a smooth grow-from-center animation (150ms ease-out)
• Uses requestAnimationFrame-driven height animation since the virtualized list uses absolute positioning
• Added show-less button to collapse expanded groups back
• Section detection uses tree node traversal (not DOM siblings) for reliability with virtualized row recycling

PR status icons

• Sessions with a PR show git-pull-request icon in the status column
• Merged PRs show git-merge icon
• Detection uses session.metadata.pullRequestUrl and session.metadata.pullRequestMerged

Compact layout options (sessions app only)

• hideSectionCount — hides the session count next to section headers
• hideSessionBadge — hides the repository badge on session cards (redundant when grouped by repo)
• useStatusOnlyIcons — icon column shows only status indicators; session type icon moves to the details row
• compactShowMore — enables the hover-reveal show-more behavior

Timestamp always visible

• Timestamp is always shown on session cards with a dot separator

Files changed

• agentSessionsControl.ts — Show-more hover logic, section map, animation, refresh resilience
• agentSessionsViewer.ts — Show-more/show-less renderers, status-only icons, section renderer options
• agentSessionsModel.ts — IAgentSessionShowLess type and helpers
• agentsessionsviewer.css — Show-more compact styles, details icon styles
• sessionsViewPane.ts — Passes new compact options to the control
• sessionsViewPane.css — Sessions-app-specific show-more line decoration styles

[Copilot]

Pull request overview

Redesigns the Agent Sessions list UI/behavior (used by the sessions app, and partially by the workbench chat view) to support compact “show more/less” interactions, PR status indicators, and additional compact layout options.

Changes:

• Added “show more” hover-reveal behavior (compact mode) and introduced a “show less” list item for collapsing expanded repository groups.
• Added status-only icon mode and PR status icons (pull request / merged) plus related styling.
• Added sessions-app-specific configuration flags and CSS overrides to enable a more compact layout in the sessions app.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
src/vs/workbench/test/browser/componentFixtures/agentSessionsViewer.fixture.ts	Updates fixture construction for the section renderer’s new options parameter.
src/vs/workbench/contrib/chat/test/browser/agentSessions/agentSessionsDataSource.test.ts	Extends datasource tests to cover the new “show less” item when expanding repository groups.
src/vs/workbench/contrib/chat/browser/agentSessions/media/agentsessionsviewer.css	Adds styling for PR status icons and the new details-row icon element.
src/vs/workbench/contrib/chat/browser/agentSessions/agentSessionsViewer.ts	Implements status-only icons, PR status icon selection, show-more/show-less renderers, and list delegate changes.
src/vs/workbench/contrib/chat/browser/agentSessions/agentSessionsModel.ts	Introduces IAgentSessionShowLess + type guard.
src/vs/workbench/contrib/chat/browser/agentSessions/agentSessionsControl.ts	Implements compact hover-driven show-more/show-less height animation and show-less click handling.
src/vs/sessions/contrib/sessions/browser/sessionsViewPane.ts	Enables the new compact options for the sessions app view pane.
src/vs/sessions/contrib/sessions/browser/media/sessionsViewPane.css	Adds sessions-app-scoped CSS overrides for compact show-more/show-less presentation.

[osortega]

Addressed all 7 review comments in commit 2a7d6f4:

1. Removed unused sessionToSection map — only sectionToShowMore is needed
2. Animation frame cleanup on dispose — registered disposable that cancels pending rAFs; guarded updateElementHeight with try/finally
3. Reduced motion support — animateHeight() checks IAccessibilityService.isMotionReduced() and sets final height immediately when enabled
4. Mid-animation collapse fix — tracks currentAnimatedHeight so collapse starts from actual current height, not fixed HEIGHT
5. Stale data-section-label fix — explicitly removes attribute when template is reused with a non-grouped or no-repo session
6. Show-more label scoped — added compactLabel option to AgentSessionShowMoreRenderer; core keeps "Show {0} More...", sessions app uses "+{0} more"
7. Magic number replaced — uses AgentSessionShowMoreRenderer.COLLAPSED_HEIGHT instead of literal 1

Also fixed lint warnings: using targetWindow.requestAnimationFrame/cancelAnimationFrame for multi-window support, and eslint-disable for justified querySelector usage on virtualized list rows.