feat(web): refine session defaults and chat affordances

[GCWing]

Summary

• Add backward-compatible fixed/follow-last defaults for the Agent Harness and remember successful ChatInput Harness selections for ordinary new sessions.
• Keep Assistant, ACP, and explicitly requested modes unchanged while moving New Session into each workspace action strip.
• Keep user-message timestamps/actions visible at rest, include seconds, and correct single-line OverflowText overflow detection.
• Update locales, account settings-sync coverage, capability source data, and generated projections.

Type and Areas

Type: Feature / UI/UX / bug fix

Areas: Web UI, design system, config contracts, Desktop/Tauri adapter, remote settings sync, interactive capability documentation

Motivation / Impact

New ordinary sessions can now either follow the last Harness explicitly selected in ChatInput or use a fixed Harness. Session creation is scoped to its owning workspace, message metadata no longer requires hover, and compact single-line labels no longer show false overflow affordances.

Persisted fields are additive. Existing default_mode_id values keep their historical fixed-default meaning, while untouched configurations adopt follow-last behavior with Standard as the initial fallback.

Verification

Passed locally:

• pnpm run fmt:rs
• pnpm --dir src/web-ui run test:run src/flow_chat/services/ChatInputModePreferenceService.test.ts src/infrastructure/config/components/DefaultHarnessConfig.test.tsx src/infrastructure/config/components/RuntimeSettingsPages.test.tsx src/flow_chat/services/flow-chat-manager/SessionModule.test.ts src/flow_chat/hooks/useSessionModeSelection.test.tsx src/flow_chat/utils/chatInputMode.test.ts src/app/components/NavPanel/sections/workspaces/WorkspaceListSectionLayout.test.ts src/app/components/NavPanel/unifiedSessionCreation.test.ts src/flow_chat/components/modern/UserMessageItem.test.tsx src/flow_chat/components/modern/UserMessageItemActions.test.ts src/shared/ui/OverflowText.test.tsx — 11 files, 184 tests
• pnpm run check:web
• pnpm run design-system:test
• pnpm run i18n:audit
• pnpm run check:repo-hygiene
• cargo test -p openbitfun-config-contracts --lib — 73 passed
• cargo test -p openbitfun-core --no-default-features --features remote-connect --lib service::remote_connect::settings_sync::tests — 7 passed
• cargo check -p openbitfun-desktop
• pnpm run capabilities:generate
• pnpm run capabilities:test — 15 passed
• pnpm run capabilities:check
• git diff --check origin/main...HEAD
• node scripts/check-git-object-sizes.mjs --base origin/main --head HEAD — 52 blobs checked, no unapproved oversized objects

pnpm run motion:audit also completed as a non-gating inventory and reported one unrelated existing SSH animation item.

No browser/manual visual validation was performed, per repository guidance; source and component tests do not prove final visual fidelity. Account settings-sync serialization and legacy compatibility were exercised, but no end-to-end remote-control session was run. Remote workspace, Peer Device Mode, Detached Dispatch, release/packaging, and real-data paths were not exercised locally.

Reviewer Notes

The default-Harness config uses additive optional fields. Removing a custom Agent clears both fixed and remembered references without deleting user configuration or silently changing a legacy fixed policy.

Checklist

• This PR is focused and does not include secrets, temporary prompts, generated scratch files, or unrelated artifacts.
• Relevant verification is recorded above, or skipped checks are explained.
• User-facing strings, docs, and locales are updated where applicable.