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fix(jq): bound object-key/index error previews with capped rendering - #2697
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…ostile values (#2699) ## What changed Bounds the CPU cost of jq math/index error previews, not just their allocation. ## Why Follow-up to #2697: that PR capped preview *allocation* with the `Capped` sink, but the sink swallowed over-budget writes with `Ok(())`, so `Val`'s `Display` (the `?`-laden `format_val!`/`write_seq!` machinery) kept expanding the full hostile value just to discard the output. For the finding's shared-structure input (`reduce range(0; 40) as $i (1; [., .]) | . + 1`, a ~2^40-element expansion on type-mismatch), the error path still walked the whole expansion. ## Before / After (production entry point, `timeout 120`, direct child timing) Before (by source inspection + failing test `preview_writer_aborts_once_over_budget`): `write!` over a 200 KB value returned `Ok` after walking all of it. After: ``` $ time ./target/debug/bashkit -c 'jq -n '\''reduce range(0; 40) as $i (1; [., .]) | . + 1'\''' jq: error (at <unknown>): array ([[[[[[[[[[[...) and number (1) cannot be added exit=5, 80-byte stderr, 0.012s wall ``` Exit code 5 matches real jq's runtime-error exit; small-value wording is unchanged (`math_errors_use_jq_wording` passes). Also fixed: over-budget previews that aborted before filling the buffer (multibyte char straddling the cut) previously returned without the `...` marker; the marker is now unconditional on over-budget output. Small-value output is byte-identical. ## Validation - `cargo test -p bashkit --lib --features jq builtins::jq`: 357 passed, 0 failed (6 new tests: early-abort, exact-fit, just-over, multibyte, recovery, huge-operand session integration) - `cargo fmt --check`, `cargo clippy --all-targets --features jq`: clean - `just check-okf`: conforms; knowledge note updated in `knowledge/runtimes/jaq-json-vendor.md` ## Checklist - [x] Tests added or updated - [x] Backward compatibility considered (internal code; error-preview bytes for small values unchanged)
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What
Error-preview rendering in
crates/bashkit/src/builtins/jq/jaq_json/jqmsg.rsmaterialized huge values before truncating:dump_trunccalledv.to_string()(full render, outside the memory meter) and truncated after.indexinterpolated the raw key string (format!("string {}", r)) into cannot-index errors.A 200 KB string key produced a ~200 KB error string; object keys built by filters (e.g.
{([range(0;200000)]): 1}) transiently rendered megabytes.Fix
dump_truncrenders through a 15-byte cappedfmt::Writesink, then applies the legacy 11-bytes+...cut. Small-value output is byte-identical.dump_trunc.knowledge/runtimes/jaq-json-vendor.md.Proof
cargo test -p bashkit --lib --features jq builtins::jq: 350 passed.cargo fmt --check,cargo clippy --features jq -- -D warnings: clean.Cannot index array with string "a",Cannot use array ([0,1,2,3,4,...) as object key); huge key error is 74 bytes.just check-okf: conformant.