Fix COMError crashes and performance in Thunderbird

[serrebi]

Thunderbird works much better

I vibe coded this. I just wanted this addon to help make Thunderbird very user friendly for blind users.

What was broken

• COMError not caught anywhere. Every property access on Mozilla objects (.role, .firstChild, .parent, .IA2Attributes, .states, .name) throws _ctypes.COMError when objects go stale during UI updates. Only AttributeError/KeyError were caught. COMErrors hit NVDA's error handler 11+ times per focus change, triggering watchdog freeze recovery (0.5–0.9s freezes).
• event_focusEntered ran expensive _IA2Relations COM call on every ancestor object in the focus chain. Also used a chain of if/if/if instead of if/elif, so every branch ran on every event.
• event_documentLoadComplete read entire message body with makeTextInfo("all").text, blocking the main thread on large HTML emails before truncating to 4000 chars.
• readPreviewPane swapped focus twice unnecessarily — called api.setFocusObject() twice just to get a tree interceptor reference, firing the entire focus event chain for no reason.
• chooseNVDAObjectOverlayClasses made redundant COM calls — accessed parent IA2Attributes even when the object's own attributes already matched.
• No auto-focus on startup — focus always landed on the preview pane (or Thunderbird's Home tab), requiring a manual Shift+Tab to reach the message list. The old shift+tab approach was unreliable due to variable focusable elements between panes.

What this PR does

• Import COMError and catch it in all event handlers, overlay class methods, and property accessors
• Restrict _IA2Relations lookup to INTERNALFRAME role only, with its own try/except and null check on objectWithFocus()
• Optimize event_documentLoadComplete: limit the text range to 4000 chars before extracting .text (collapse + move end point), avoiding full virtual buffer processing
• Optimize readPreviewPane: try obj.treeInterceptor and getTreeInterceptor() first, only fall back to the double focus swap if neither returns a tree interceptor
• Optimize chooseNVDAObjectOverlayClasses: check obj.IA2Attributes first and short-circuit — only query parent attributes if the object's own xml-roles doesn't match
• Reliable auto-focus on startup: schedule a 4-second delayed focus attempt (after Thunderbird's Home tab finishes and Inbox tab loads), then use F6 pane cycling with retry (up to 4 attempts) to land on the message list. Verifies landing by checking for threadTree-row* IA2 ID prefix (distinguishes message list from folder tree). Falls back gracefully if inbox hasn't loaded.

Testing

Manually tested with Thunderbird Daily 150.0a1 (2026-03-15) (64-bit) and NVDA 2026.1beta6.

🤖 Generated with Claude Code