fix: C allocator contract, shadertoy overloads/MSL stride, minidumps

Closes the remaining library rows of the final completeness audit
(docs/rewrite/notes/final-Z3.md):
- libghostty-vt: OSC parser storage goes through the caller-supplied C
  allocator via a ByteStorage abstraction; ghostty_osc_new reports
  GHOSTTY_OUT_OF_MEMORY and failed grows invalidate the OSC like Zig.
  Tested with a counting/failing/limiting C allocator.
- shadertoy: sampler parameter rewriting is keyed by full signature so
  overloads work; the Metal uniform block keeps std140 strides for
  iChannelTime[4] (MSL offsets checked against the upload layout).
- tripwire.zig ported (named trip points, hit counts, verification) and
  used to port the previously skipped allocation-failure tests that have
  a fallible Rust path; the rest are documented.
- crash: fatal signals capture siginfo + registers and a forked helper
  writes a minidump (minidump-writer) as an envelope attachment, like
  sentry-native/Breakpad; tests parse it with the minidump crate.
- kitty LoadingImage::debug_dump (debug builds) and the Darwin
  Instruments signpost around benchmark runs.

Test Plan:
- cargo test -p ghostty-vt-capi --test c_allocator
- cargo test -p ghostty-crash --test minidump

crates/ghostty-terminal/src/tabstops.rs

@@ -59,6 +59,13 @@ pub struct Tabstops {
     dynamic_stops: Vec<Unit>,
 }
 
+/// Failure points of [`Tabstops::resize`] (Zig: `resize_tw`).
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+enum ResizePoint {
+    DynamicAlloc,
+}
+crate::tripwire_module!(resize_tw, ResizePoint, TryReserveError);
+
 impl Default for Tabstops {
     fn default() -> Self {
         Self {
@@ -141,6 +148,7 @@ impl Tabstops {
         }
 
         // Allocate first so that failure leaves our state untouched.
+        resize_tw::check(ResizePoint::DynamicAlloc)?;
         let mut new: Vec<Unit> = Vec::new();
         new.try_reserve_exact(size)?;
         new.resize(size, 0);
@@ -175,6 +183,7 @@ impl Tabstops {
 #[cfg(test)]
 mod tests {
     use super::*;
+    use crate::tripwire::ResetMode;
 
     #[test]
     fn tabstops_basic() {
@@ -238,7 +247,21 @@ mod tests {
         assert_eq!(9, count);
     }
 
-    // "Tabstops: resize alloc failure preserves state" is skipped: it uses
-    // Zig tripwire allocation failure injection. The Rust resize allocates
-    // before mutating, so a failure leaves `cols` unchanged by construction.
+    #[test]
+    fn tabstops_resize_alloc_failure_preserves_state() {
+        // If resize() fails during allocation, the original cols value is
+        // preserved (not corrupted).
+        let mut t = Tabstops::new(80, 8).unwrap();
+        let original_cols = t.cols;
+
+        // Trigger allocation failure when resizing beyond prealloc
+        let oom = Vec::<u8>::new().try_reserve(usize::MAX).unwrap_err();
+        resize_tw::error_always(ResizePoint::DynamicAlloc, oom.clone());
+        let result = t.resize(PREALLOC_COLUMNS * 2);
+        assert_eq!(Err(oom), result);
+        resize_tw::end(ResetMode::Reset).unwrap();
+
+        // cols should be unchanged after failed resize
+        assert_eq!(original_cols, t.cols);
+    }
 }