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terminal: bounds check params in DCS passthrough entry - #11088
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When a DCS sequence has more than MAX_PARAMS parameters, entering dcs_passthrough would write to params[params_idx] without a bounds check, causing an out-of-bounds access. Drop the entire DCS hook when params overflow, consistent with how csi_dispatch handles it. Found by AFL fuzzing.
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This adds a `test/fuzz-libghostty` which is a standalone `zig build` target for building an AFL++ instrumented executable for fuzzing the libghostty-vt parser. I also added a `pkg/afl++` (based on zig-afl-kit) so instrumenting objects and using AFL++ is a bit easier. Fuzzing `libghostty-vt`'s parser is as easy as `zig build run`, but see the README for a lot more details. I ran the fuzzer for ~14 hours total and only found one crash #11088. I'm pretty confident at this point our Parser layer isn't obviously crash-able, but need to instrument more places to fuzz. We don't use Zig's built-in fuzzing yet because as of 0.15 (our current stable), it isn't ready and AFL++ is an industry proven tool to do this.
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When a DCS sequence has more than MAX_PARAMS parameters, entering dcs_passthrough would write to params[params_idx] without a bounds check, causing an out-of-bounds access. Add the same guard that csi_dispatch already has.
Found by AFL fuzzing, test and fix produced by Codex.