fix(interpreter): Box::pin expand_word to prevent stack overflow in nested $()#1109
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fix(interpreter): Box::pin expand_word to prevent stack overflow in nested $()#1109
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…ested $() Each command substitution level previously inlined the expand_word async state machine into the caller's stack frame. The state machine is large (many WordPart match arms with their locals) and at ~20-30 nesting levels the call stack overflows with SIGABRT. Fix by boxing two key futures: - expand_word: wraps the inner implementation in Box::pin so each call allocates its future on the heap instead of the parent's stack - execute_cmd_subst: new helper that Box::pin-s the command substitution body (state snapshot, command loop, state restore), keeping those large locals off the stack With both futures boxed, each nesting level uses constant stack space regardless of depth. The default max_subst_depth of 32 now completes without overflow (previously crashed at ~20). Closes #1089
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Summary
expand_wordand extractexecute_cmd_substhelper to prevent stack overflow from nested command substitutions$(...)level previously inlined the largeexpand_wordasync state machine into the caller's stack frame, causing SIGABRT at ~20-30 levelsmax_subst_depth) now completes safelyChanges
interpreter/mod.rs: convertexpand_wordfromasync fntofn -> Pin<Box<Future>>wrapper overexpand_word_inner; addexecute_cmd_substBox::pin-ed helper for the command substitution bodystack_overflow_regression_tests.rs: 2 tests exercising depth 32 and nested arithmetic substitutionspecs/006-threat-model.md: add TM-DOS-089Test plan
cargo test --test stack_overflow_regression_tests— 2 new tests pass (previously SIGABRT)cargo test --all-features -- --skip ssh_supabase— all passcargo clippy --all-targets --all-features -- -D warnings— cleanCloses #1089