A PatchOptions.fast_capture pass reads each bad range ONCE at the full batch and
leaves every FAILED block NonTrimmed for a later pass — no bisect, no per-sector
grind, no retry. This lets a first retry pass grab the readable blocks (the
sweep's good skip-ahead overshoot) of EVERY section quickly, before any single
section's slow per-sector recovery — instead of grinding section 1 to exhaustion
before even touching section 2. A later pass (fast_capture = false) does the
granular bisect/retry on what's left.
Load-bearing invariant (fixture test): NO data is dropped. A failed block becomes
NonTrimmed (pending, retried by a granular pass), NEVER Unreadable. The test pins
that the readable half of a range recovers, the bad half stays NonTrimmed (not
Unreadable), and the bad block is marked in ONE batch read with zero bisection.
Disc::copy's internal patch keeps fast_capture=false (single-call full recovery).
Live drive probing (cold-single vs in-stream batch vs centered window,
one clean uncached read per sector) showed recovery RATE is identical
across approach: 3/5 every mode. The drive's per-sector ECC is
media-bound and partly stochastic, NOT approach-bound. So scatter
(seek-away recalibration + far-anchor re-read) does not improve recovery
and is dead weight — removed (function, read_good_sectors, SCATTER_*
consts, and its tests).
Add SubRanges: the still-bad (pos,len) sub-ranges of a section with
remove()/split, the work-list foundation for the upcoming per-section
recovery decomposition (recover_section -> stream/bisect/retry phase
helpers). Unit-tested; unused until the decomposition lands.
25 patch + 8 AB profile tests green; precommit clean on Rust 1.86.
The 'reset, read good data, come back for one sector' technique. A
genuinely-damaged sector makes the drive grind its full recovery timeout
and still fail; re-reading consecutive bad LBAs at identical conditions
re-fails AND is the rapid-failure cadence that drops the BU40N into a
firmware fast-fail wedge (CLAUDE.md hard-rule #2).
scatter_recover: on a stuck single sector, make up to SCATTER_MAX_ATTEMPTS
fresh tries, each preceded by read_good_sectors() — a seek to a far
known-good anchor + a sustained read that re-seats the head/servo and
breaks the failure cadence. The fresh re-read uses the FAST timeout
(recovery=false) so a recalibrated marginal sector reads quick and a
truly-dead one fails fast instead of burning 60s per attempt. The seek +
good read IS the settle (matches ddrescue/MakeMKV) — no idle sleep.
Gated to genuine single-sector MEDIUM_ERROR (0x03): transport faults
still abort the pass, NOT_READY keeps its own retry path, wedge-family
senses are left for cooldown/eject. A scatter recovery is recorded
exactly like a normal read success (write-then-mark-Finished); nothing
marks a range good without a successful read + write.
Logs anchor_ms/reread_ms per attempt for live tuning. 5 fixture tests
(recover-marginal, give-up-dead, skip-non-medium, skip-batch, AACS
widen); 2 AB read-count guards raised for scatter's bounded extra reads.
Precommit green on Rust 1.86.
Matthew Jackson