fix(renderer): prevent render loop stall by re-checking immediateRerenderRequested in loop() finally block

[AH64-dll]

Problem

The render loop can silently stall in idle mode (_isRunning = false) when a requestRender() call arrives in the window between the if/else scheduling decision and the finally block that sets this.rendering = false.

Race condition

1. loop() runs, at the scheduling decision sees _isRunning = false and immediateRerenderRequested = false -> goes to else branch, clears timeout, schedules nothing
2. Between the else branch and the finally block, a requestRender() fires -- rendering is still true -> only sets immediateRerenderRequested = true and returns early (line 1507-1509)
3. finally sets this.rendering = false but does not check immediateRerenderRequested
4. activateFrame() finally sets this.updateScheduled = false
5. No timeout was scheduled, and the flag is set but nobody checks it
6. Render loop is dead until an external event (SIGWINCH, mouse, keyboard) triggers another requestRender()

This manifests as the TUI going black during burst event processing (e.g. when the user presses Enter to submit a prompt and the agent starts working).

Fix

In loop()'s finally block, re-check immediateRerenderRequested. If it was set during the race window (after the scheduling decision but before rendering = false), re-issue via setImmediate.

setImmediate (not process.nextTick) is needed because activateFrame() keeps updateScheduled = true until its own finally after loop() returns. process.nextTick fires before microtasks resume -- before activateFrame's finally -- so requestRender() would be blocked by the !updateScheduled guard.

Related

• OpenCode issue TUI screen goes completely black when agent starts working (render loop silently stalls) opencode#37803 (black screen when agent starts working)
• OpenCode issues #32361, #33887, #35494 (related black screen reports)
• Original closed PR fix(core): reschedule when requestRender races the loop scheduling #1086 (similar approach, this is a re-submission)