fix(streaming): preserve routed byte output and enforce builtin budgets

[chaliy]

What changed

Streaming builtin readers now charge the shared input budget and admit record/collector storage before growth. Live execution delivers saved stdout/stderr descriptors through the awaited output pumps, preserves raw bytes in input process substitutions, and keeps streaming utilities live through descriptor/file redirects. Background output completing at shell exit drains before execution closes, including scripts without an explicit wait.

Why

Bounded pipes did not bound growing records or account for streamed input. Saved descriptor output could disappear from live execution, <(...) decoded binary data through a shell-text boundary, and adding 2>&1 could make a final filter wait for producer completion.

Before / After

• A long record exceeding the live-memory cap, and streamed input exceeding the aggregate byte cap, now fail with the corresponding typed resource error; the session remains reusable.
• exec 3>&1 >out; echo hi >&3: live stdout was empty; now sinks and capture receive hi\n, subject to output caps and sink errors.
• cat <(printf '\377\000A'): output was ef bf bd 41; now it is ff 00 41, matching Bash.
• Gated producers through cat 2>&1 and grep first 2>&1 now deliver their first output before the producer can finish.
• A delayed background command ending after the final script boundary now delivers stdout/stderr exactly once to live sinks and capture. Previously its output was missing unless the script explicitly waited.

Existing buffered process-substitution, utility, background-job and tool-queue limitations remain documented.

Risk

• Medium: builtin output routing and request accounting affect pipelines and redirects. Buffered options and diagnostics use the same already-open destinations, avoiding repeated truncation.
• Regression coverage includes redirect permutations against Bash, saved-fd ordering, closed descriptors, caps, sink failure, binary substitutions, budget rejection/recovery and final background draining.

Validation

• Local just pre-pr and just test passed using the container's provided Linux subreaper: 3,885 core unit tests, 2,591 integration tests (four existing ignores), and 19 failpoint tests, plus workspace/doc/script checks.
• cargo clippy --all-targets --all-features -- -D warnings passed.
• Nine audit regressions pass. Five CLI byte/status comparisons match GNU Bash, including delayed background completion.
• The 96-case Bash comparison benchmark reports zero errors and 100% matching output. Parallel and SQLite benchmark workloads completed.

Checklist

• Tests added or updated
• Backward compatibility considered

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Status	Name	Latest Commit	Preview URL	Updated (UTC)
✅ Deployment successful! View logs	bashkit	c090e75	Commit Preview URL Branch Preview URL	Oct 18 2026, 11:42 PM