if (pos in seen) { disc++ } # first-arrived-byte-wins
Done. I diagnosed the failure modes, implemented a verified reassembler, and wrote the full write-up to ~/SOLUTION.md (script at ~/tcp_reassemble.sh).
Naive solutions fail because they either (a) sort segments by seq and concatenate — which double-counts retransmitted bytes and cannot do first-arrived-byte-wins, or (b) append on arrival — which emits future bytes ahead of a hole. Segment-level dedup also fails on partial overlaps, and looping over sequence numbers to count gaps hangs on large absolute sequence spaces.
Key bytes by absolute position, keep the first byte seen at each position, then read out only the contiguous prefix and count holes as jumps in the sorted position set. len<=0 is ignored; a checked len vs hex/2 guards truncated payloads.
Pipeline: awk (arrival-ordered, per-byte first-wins + discard count) → sort -k1,1 -k2,2n → awk (contiguous emission + gap-jump count) → sha256sum.
# pass 1
if (pos in seen) { disc++ } # first-arrived-byte-wins
else { seen[pos]=1; print "1 " pos " " byte }
# pass 2
if (pos == prev+1) { if (emitting) out = out byte }
else if (pos > prev+1) { gaps++; emitting = 0 }
Output is 4 lines: hex, sha256, discarded bytes, unresolved gap regions. Direction is auto-selected (busiest src>dst) or passed explicitly. Runtime uses only bash/awk/sort/sha256sum.
Note on convention: default HASH=hex hashes the hex text; HASH=bytes hashes the reconstructed raw bytes (printf '%b' "\\x..").
HASH=hex and HASH=bytes vs hashlib).FUZZ OK: 400 random traces matched reference and RAW+HEX HASH OK: 120 traces.Full details, test table, and exact commands are in ~/SOLUTION.md.
# Evidence - Problem class: tcp-stream-reassembly-overlapping-retransmits - Model: openrouter/deepseek/deepseek-v4.1-flash - Solved: 2026-09-16T16:16:06.589Z - Verification: solution produced by pi in sandbox; see signatures.json
{"description": "Reassemble the TCP byte stream for one flow from a text packet trace using only bash/awk/sort/sha256sum (no python/perl). Each line is: ts src>dst flags seq len ack payload_hex. Required behaviour: out-of-order arrival is resolved by absolute sequence position; a retransmitted segment that overlaps already-delivered bytes is deduplicated with FIRST-ARRIVED-BYTE-WINS for the overlapping region and the non-overlapping tail appended; pure duplicate/keepalive segments (len 0 or fully covered) contribute nothing; and bytes for positions greater than (highest contiguous seq seen + receive window) must be buffered, not appended, until the gap is filled. Output: the contiguous stream as hex, its sha256, the count of bytes discarded as duplicate/overlap, and the count of gaps still unresolved at trace end.", "environment": "bash", "language": "shell", "model": "openrouter/deepseek/deepseek-v4.1-flash", "problem_class": "tcp-stream-reassembly-overlapping-retransmits", "provider": "openrouter", "solved_at": "2026-09-16T16:16:06.589Z", "version": "5.2"}Done. I diagnosed the failure modes, implemented a verified reassembler, and wrote the full write-up to ~/SOLUTION.md (script at ~/tcp_reassemble.sh).
Naive solutions fail because they either (a) sort segments by seq and concatenate — which double-counts retransmitted bytes and cannot do first-arrived-byte-wins, or (b) append on arrival — which emits future bytes ahead of a hole. Segment-level dedup also fails on partial overlaps, and looping over sequence numbers to count gaps hangs on large absolute sequence spaces.
Key bytes by absolute position, keep the first byte seen at each position, then read out only the contiguous prefix and count holes as jumps in the sorted position set. len<=0 is ignored; a checked len vs hex/2 guards truncated payloads.
Pipeline: awk (arrival-ordered, per-byte first-wins + discard count) → sort -k1,1 -k2,2n → awk (contiguous emission + gap-jump count) → sha256sum.
# pass 1
if (pos in seen) { disc++ } # first-arrived-byte-wins
else { seen[pos]=1; print "1 " pos " " byte }
# pass 2
if (pos == prev+1) { if (emitting) out = out byte }
else if (pos > prev+1) { gaps++; emitting = 0 }
Output is 4 lines: hex, sha256, discarded bytes, unresolved gap regions. Direction is auto-selected (busiest src>dst) or passed explicitly. Runtime uses only bash/awk/sort/sha256sum.
Note on convention: default HASH=hex hashes the hex text; HASH=bytes hashes the reconstructed raw bytes (printf '%b' "\\x..").
HASH=hex and HASH=bytes vs hashlib).FUZZ OK: 400 random traces matched reference and RAW+HEX HASH OK: 120 traces.Full details, test table, and exact commands are in ~/SOLUTION.md.
# Evidence - Problem class: tcp-stream-reassembly-overlapping-retransmits - Model: openrouter/deepseek/deepseek-v4.1-flash - Solved: 2026-09-16T16:16:06.589Z - Verification: solution produced by pi in sandbox; see signatures.json
{"description": "Reassemble the TCP byte stream for one flow from a text packet trace using only bash/awk/sort/sha256sum (no python/perl). Each line is: ts src>dst flags seq len ack payload_hex. Required behaviour: out-of-order arrival is resolved by absolute sequence position; a retransmitted segment that overlaps already-delivered bytes is deduplicated with FIRST-ARRIVED-BYTE-WINS for the overlapping region and the non-overlapping tail appended; pure duplicate/keepalive segments (len 0 or fully covered) contribute nothing; and bytes for positions greater than (highest contiguous seq seen + receive window) must be buffered, not appended, until the gap is filled. Output: the contiguous stream as hex, its sha256, the count of bytes discarded as duplicate/overlap, and the count of gaps still unresolved at trace end.", "environment": "bash", "language": "shell", "model": "openrouter/deepseek/deepseek-v4.1-flash", "problem_class": "tcp-stream-reassembly-overlapping-retransmits", "provider": "openrouter", "solved_at": "2026-09-16T16:16:06.589Z", "version": "5.2"}