v0.1.1147 Aug 2026·DevTools, Tabs & interface

DevTools debugger: pause on exceptions

The debugger gains its second breakpoint kind, and the one every developer reaches for after `debugger;`: pause on exceptions. Arm it to 'all' or 'uncaught' and the engine captures the moment a JavaScript error is thrown - the thrown value's message, the function it happened in, and every local and block variable at its real value right at the throw, before the stack unwinds. It hooks the single point every throw in the engine passes through, so it is complete by construction (no missed throws) and free when disarmed: ordinary try/catch code pays nothing. 'uncaught' mode ignores a throw that a try/catch handles and stops only on one that escapes; 'all' stops on both. The visual Debugger panel gets a none/uncaught/all switch and shows the thrown error in red above the paused scope. DevTools moves 24 to 25; overall holds at 51.

Parity with the reference browser

74overall, as of v0.1.343

Web APIs / DOM surface42

Security architecture66

GPU / graphics acceleration68

DevTools / extensions72

Networking85

Media85

Accessibility85

Real-world site compatibility99

HTML parsing100

CSS parsing + selectors100

Layout: block / flex / grid / tables / writing-modes100

Paint + visual100

JavaScript language100

JavaScript performance (JIT)100

HTML parsing100

What changed 3 changes

DevTools	Pause on exceptions: a new debugger mode (none / uncaught / all) captures the live scope and the thrown value at the moment an error is thrown. It hooks the one place every throw in the engine funnels through (the raise path that also attaches stack traces), so no throw is missed, and it reads the scope BEFORE the stack unwinds - the paused frame shows the thrown message plus every local/block variable at its value. Verified: a thrown Error under 'all' is captured with reason, message and a local (code=500) even through a try/catch; 'uncaught' ignores a handled throw and stops on an escaping one; default off pauses on nothing.
DevTools	It is free when off and independent of the `debugger;` domain: the hook is a single fast flag check on the throw path, so normal try/catch control flow is untouched (conformance gate 6375/6375 unchanged), and pause-on-exceptions works even on a page with no `debugger;` statement, exactly as the reference browser does.
Tabs & interface	The visual Debugger panel gains a none / uncaught / all switch, and a paused-on-exception shows the thrown error in red above the scope chain. Exposed through the CDP `Debugger.setPauseOnExceptions` method, a `__debug_pause_exceptions` native, and the shell `engine_session_debugger_control` command. 3 new engine tests (13 in the debugger module), gate 6375/6375 with native-JIT and no-nanbox green; shell typechecks + compiles.