[Bug]: PiP reflows chat and is constrained to the right-hand lane after V2 #14929

Problem

After the V2 orchestrator merge, browser/device picture in picture no longer behaves like a freely movable overlay over the conversation. Dragging it left is constrained to a lane on the right, and moving or resizing it shifts and narrows both the messages and the input field.

I actively want the old floating behavior back for most cases. Keeping a preview visible while reading or typing should not rearrange the conversation underneath it.

Steps to reproduce

1. Open a thread with enough text to see line wrapping. Keep the main sidebar open and use a 1440×900 window.
2. Open a browser preview or simulator in the right panel and float it over chat. For a simulator: More device actions → Float device over chat.
3. Compare its default position with 0.45. Drag it left and right, then up and down. Resize it from its west edge.
4. Watch the messages and input field. Repeat at 1920×1080 with the thread-details card open to see how it shares space with PiP.

Expected behavior

Restore floating PiP as the default: movable across the chat canvas, above the messages, with the text and input keeping their position and width. The existing canvas bounds and protection around the input can remain.

An explicit Dock button could make the current reflow behavior useful as an opt-in mode. Undock should return it to the floating overlay. Docking should be a choice; simply opening or dragging PiP should not opt me into reflow.

Actual behavior

At 1440×900, the same leftward gesture leaves the 0.45 input at x=477, width=742px. In 0.46, PiP stops at x=928, and the input moves from x=453, width=710px at the default PiP position to x=289, width=614px. These are CSS pixels from the page origin. Baseline widths differ between releases; the regression is the position/width changing within the same version as PiP moves.

Versions and verification

• Before: v0.0.45 / 6c8fed35dd.
• After: v0.0.46-preview.20261002.2598 / b37fcea42f.
• Introduced on main with feat(orchestrator): introduce new orchestrator #2829 (de34391427). The 0.45 preview channel already included the new layout, so the stable 0.45 tag is the baseline here.
• Captured on macOS using an iPhone 17 Pro simulator stream inside the web client in T3's internal browser, with identical sample conversations and isolated state. No native mobile app was tested.
• The recordings use synthetic pointer gestures through the actual PiP drag/resize handlers, with native pointer-capture bookkeeping bypassed. They demonstrate layout behavior, not manual hit-target ergonomics.
• Simulator PiP was directly exercised. Browser PiP uses the same MiniPlayerShell and layout functions; desktop native always-on-top PiP was not tested.

Relevant source

The new chat canvas layout reserves a minimum chat lane while dragging and derives the chat insets from PiP's frame. Thread details participate in the same placement. The 0.45 PiP shell instead measures the canvas/composer and floats without changing chat layout.

Before/after screenshots and movement recordings are attached below.