itd-155 ac-1 narrowed: the galloping adjacency probe (internal/adapter/scanner/scanner.go gallopingFind) grows under a per-line budget of 4*len(line)+4096 bytes and, once that budget is spent, keeps the fixed 512-byte window it already has — so on a line engineered to grow the window at many junctions a match end can again be a truncation artefact of the window edge, the shape iss-189/iss-190 were about. A single long token always fits the budget. The trade-off (a measured quadratic cliff without the cap) is recorded in code only; the intent promises 'never a truncation artifact' unconditionally, so the promise or the record should say where the guarantee ends

Frontmatter

.abcd/work/issues/open/iss-2609230949465250-itd-155-ac-1-narrowed-the-galloping.md
open on GitHub ↗ · commit history ↗

mentions3

• iss-189adjacency probe's trailing \b can be satisfied by the window edge instead of real content, causing a spurious over-redaction. scanAllPatterns (scanner.go) slices the line to a bounded window (line[end:min(end+512,len(line))]) before running each pattern's adjacencyProbe, to keep one probe attempt's cost constant regardless of what follows (iss-185's fix). Some probes retain an internal trailing \b of their own (e.g. net_lan_hostname's `\b` at the very end of its alternation) which normally requires a real non-word character (or true end of string) after the match. But when the probe is truncated to the window, "end of window" is treated by the regex engine exactly like "end of string" — so if the window happens to end immediately after what LOOKS like a complete hostname/token, the trailing \b is satisfied by the artificial window boundary rather than by real surrounding content, even though the FULL, untruncated line would not have matched there (the real next byte continues the token). Concrete repro: a line built as `"AKIA"+16*"Q"` (a confirmed match, establishing the probe's junction) + 506 filler bytes + ".local" + "zzz" — the window (512 bytes from the junction) ends exactly after "local", so net_lan_hostname's probe matches "b...local" (satisfied by end-of-window) even though the real line continues with "zzz" right after ".local", meaning the FULL line's own un-windowed net_lan_hostname pattern would NOT match there at all (no real word boundary follows in the actual text). Impact: a spurious net:lan_hostname finding (warn severity only, not hard_fail) causes Redact to needlessly rewrite up to 512 bytes of legitimate content as fingerprinted/starred output — not a security leak (over-redaction, not under-redaction) but a correctness/usability defect: legitimate file content gets mangled on a contrived but reachable input shape. Suggested fix (from the reviewer that found this): when a probe match's end lands exactly at the window's limit AND limit < len(line) (i.e. the window was actually truncated, not naturally at the line's end), re-run that one probe against the full, untruncated line[end:] before accepting the match — paying the larger cost only in this rare edge case rather than on every probe. Found during a merge-gate correctness review of iss-185's PR (bugfix/iss-185-scanner-adjacent-secret-boundary-bypass); non-blocking (contrived input, warn-severity-only impact), so not fixed inline — captured for its own verify-and-fix cycle.
• iss-190scanner adjacency recovery is capped by maxAdjacencyProbeWindow, so a recovered token longer than the window is truncated — and the truncation can break the recovery CHAIN, hiding a third abutting token entirely. probeAt (scanAllPatterns, internal/adapter/scanner/scanner.go) runs its anchored probe against line[at:at+maxAdjacencyProbeWindow] (512 bytes), so a recovered open-ended match longer than that is recorded with an artificial end at the window edge. Two manifestations. (a) Known and accepted since iss-185: the recovered token's far tail past the window stays raw in Redact's output; the token's prefix is still masked, so this is a partial-redaction trade, not a total miss. (b) NEW, found by two independent adversarial reviews of iss-188's fix: because the artificial end does not align with the token's real end, the next iteration's probeAt(m.end) and stolenJunctions both start from a byte offset that is inside the token rather than at its junction, so the chain that would otherwise unwind a run of three or more abutting tokens breaks — the third token becomes entirely invisible, not merely truncated. Repro: line := "ghp_" + strings.Repeat("a",36) + "ghp_" + strings.Repeat("m",600) + "ghp_" + strings.Repeat("z",36) yields exactly 2 token:github_pat findings where an unbounded search would find 3; the third token's 36 raw bytes survive Redact and the fail-closed residual re-scan reports the output clean. A sharper variant of (a) affects jwt_shaped specifically: its regex requires two literal '.' separators, so a JWT-shaped token whose header and payload together exceed the window has NEITHER separator inside the probe's slice and the anchored probe finds no match at all — the token is missed entirely rather than truncated, e.g. a fixed-length match immediately followed by a JWT whose first two segments total more than ~502 bytes. This is NOT a defect introduced by iss-188's backward search; it is the same pre-existing maxAdjacencyProbeWindow trade-off from iss-185, now reachable through a second code path because the backward search feeds more candidates into probeAt. Fixing it properly needs a different mechanism (a growing or adaptive window, or re-probing chained from a recovered match's real end) that must not reintroduce the unbounded per-match cost the window exists to prevent — the exact risk iss-188's own ledger entry warned against. Deliberately not folded into iss-188's fix pass to keep that diff scoped to the confirmed junction-search defect.
• itd-155implement the galloping/exponential-doubling probe (trueMatchEnd) that replaces the fixed 512-byte adjacency window in scanAllPatterns/probeAt: the window grows only while a match keeps running into its edge and stops the moment the match ends short of the edge or reaches the real end of line, so a match end is never a truncation artifact. This is the structural fix designed in the 2026-08-08 decision [dcn-2608080000000001](../../../work/decisions/dcn-2608080000000001-iss-189-iss-190-shared-root-cause.md) after bug-hunt rounds 6-8 each BLOCKed on local patches for the same root cause (a truncated window-edge view driving a discard/skip decision reaching further than the ambiguity). It dissolves iss-189 (trailing boundary satisfied by the artificial window edge, spurious over-redaction) and iss-190 (window-capped recovery truncating a token and breaking the recovery chain) outright, without reintroducing the round-6 cost regression: the window grows only for matches genuinely still growing, at the amortized cost class the top-level unbounded match already pays. iss-189 and iss-190 (both superseded by this capture) are its acceptance corpus: their repro shapes must pass without a boundary classifier or a clipped-so-skip special case.