[6/7] feat: reuse workspace context and navigate agent output

[BIackFIame]

Summary

Part 6/7 of the CanvasTTY agent-workflow series. Context previews, session snapshots, presets, output search, deliberate shared input and layout actions make workspaces easier to resume and navigate. Approved project memory is delivered through the existing plugin API. This part also includes renderer/loading fixes and the source Electron dependency update.

Review scope and dependencies

Depends on: #135.

This is a cumulative upstream PR: GitHub's Files changed tab includes earlier unmerged parts because all PRs target upstream main; cross-fork stacked bases are unsupported. Review this part in the isolated predecessor-to-head diff. The intended merge order follows the numbered series; do not merge a later part independently of its predecessors.

The Context plugin owns memory storage and tools; its main is published at 63458cf.

Validation and current blockers

Tested feature head: e2c0b767ae2c5c91e20e13daa5f2a654aaf6029e. Local helpers, typecheck, build and secret audit passed; full suite: 2,022 passed, 10 skipped, zero failures. Historical fork CI passed on macOS, Linux and Windows using the exact candidate tree under a temporary workflow overlay. That overlay is not included here.

Draft: merge preview against updated upstream 6faadcdc found conflicts in src/preload/index.ts, src/renderer/src/features/workspace/WorkspaceCanvas.tsx, src/shared/contracts.ts. These historical results do not validate a conflict-resolved integration with current main. Preserve the newly accepted material/terminal-link behavior, resolve the overlaps, and rerun checks before marking ready.

Historical fixtures covered approved memory delivery and one output-search match. Snapshot/preset, broadcast and layout behavior have automated coverage; the full visible-app workflow and a ten-terminal search benchmark were not repeated.

Series order

1. macOS clipboard
2. Orchestration, reviews and budgets — Draft
3. Worktrees and checkpoints — Draft
4. Timeline, usage and attention — Draft
5. Network policies and temporary secrets — Draft
6. Workspace context and navigation — Draft
7. Experimental routing, handoff and remote controls — Draft

Parts 2–7 are cumulative Draft PRs against upstream main, with an isolated layer diff in each description. Their tested feature heads currently conflict with newer upstream changes; integration and fresh checks are required before readiness. Part 7 also retains its independent experimental acceptance gate.

[BIackFIame]

@codex review

Please review this PR for correctness, regressions and security issues. Review only; post findings on GitHub without changing code.

This is part 6/7 of a cumulative series. Focus on changes introduced after predecessor 9eb11095d6900c999a09b7d8e2da8ace953643e8 through current head e2c0b767ae2c5c91e20e13daa5f2a654aaf6029e, including their interactions with the inherited code. The isolated layer diff is linked in the PR description. Known merge conflicts with newer main are already documented; look for substantive code defects in addition to those integration blockers.