💡 Change Scope

• Small Change: Fast feedback, localized UI/logic, low-risk.
• Large Change: New feature, cross-boundary logic, runtime-risk (persistence, IPC, lifecycle, recovery).

📝 What Does This PR Do?

Fixes terminal display calibration auto-reference when the workspace canvas is zoomed, and stabilizes terminal zoom-settle behavior so embedded terminal content no longer intermittently “twitches” in size during viewport zoom.

The calibration fix now makes automatic shared-reference capture use the same stable baseline measurement contract as manual Set Reference, instead of sampling transformed live terminal metrics. The zoom fix keeps DPR/output sync deferred until viewport interaction settles, reducing repeated content-size churn during active zoom gestures.

This PR also adds regression coverage for the zoomed auto-calibration path and hardens two unrelated drag E2Es that flaked during validation.

🏗️ Large Change Spec (Required if "Large Change" is checked)

1. Context & Business Logic

• Auto shared reference previously diverged from manual reference when canvas zoom was active because it measured transformed live terminal output.
• Terminal zoom could trigger unstable effective-DPR/output churn while viewport interaction was still active, surfacing as intermittent terminal content size twitching.
• The intended behavior is: auto and manual reference capture must agree for the same font profile, and terminal zoom should settle to a crisp result without unstable intermediate rescaling.

2. State Ownership & Invariants

• Settings renderer owns terminalDisplayReference persistence; mounted terminal measurements are runtime observations only.
• Terminal node presentation owns viewport-interaction settle gating for DPR/output synchronization.
• Invariant: automatic shared reference and manual shared reference must be derived from the same untransformed baseline measurement contract for a given terminal font profile.
• Invariant: active viewport interaction must not repeatedly churn terminal effective DPR; the terminal applies the settled zoom update after interaction clears.
• Invariant: terminal hydration/reload behavior must preserve mounted xterm state without remount-driven blur, geometry drift, or scrollback loss.

3. Verification Plan & Regression Layer

• Unit: tests/unit/contexts/terminalDisplayReferenceAutoCapture.spec.tsx and useTrackpadGestures.spec.tsx cover the new auto-capture contract and settle timing.
• E2E: added tests/e2e/settings.terminal-display-calibration.spec.ts to prove auto shared reference matches manual capture under zoom.
• E2E: tests/e2e/workspace-canvas.terminal-device-pixel-ratio.spec.ts, tests/e2e/workspace-canvas.trackpad-gestures.spec.ts, and repeated workspace-canvas.persistence reload verification cover the zoom/twitch path.
• Flake hardening: workspace-canvas.sidebar-drag-reorder.spec.ts and workspace-canvas.spaces.overlay-drag.spec.ts now use stable client-rect drag points and longer settle windows.

✅ Delivery & Compliance Checklist

• My code passes the ultimate gatekeeper: pnpm pre-commit is completely green.
• I have signed the CLA if required (see CLA.md).
• I have included new tests to lock down the behavior (or explicitly stated why it is untestable).
• I have strictly adhered to the DEVELOPMENT.md architectural boundaries.
• I have attached a screenshot or screen recording (if this touches the UI).
• I have updated the documentation accordingly (if adding a feature or changing a contract).

Current validation note: all terminal-related unit/E2E coverage listed above passed locally. Full pnpm pre-commit was blocked by unrelated agent E2E failures outside this change scope, including workspace-canvas.agent-last-message-copy.opencode.spec.ts and workspace-canvas.agent-status-watcher.spec.ts.

📸 Screenshots / Visual Evidence

Not attached in the CLI-created PR body. Terminal-specific Playwright evidence is available locally from validation runs, and I can add UI captures in the GitHub UI if needed.