Pass 1 sweep was grinding through damage zones because the marginal-
media handler returned `Bisect` for every failed 32-sector batch —
forcing 32 single-sector reads per bad block at ~5s each on a real
BU40N-vs-Dune-Pt-2 trace. AND the JumpAhead trigger required a 16-
block damage window to fill before firing, so entry into a
contiguous damage zone took ~40 minutes of grinding before the
first jump fired. Architecturally wrong: Pass 1's job is "fast and
accurate, get the most data in the shortest time." Bisection +
recovery is Pass N's purpose-built role.
ReadCtx now carries two new fields:
- `consecutive_outer_failures: u64` — outer-batch failures since
last outer success. Bisect inner failures don't count.
- `bisect_on_marginal: bool` — whether to return Bisect on a
marginal-media batch failure.
- `fast_jump_threshold: u64` — outer-failures count that triggers
JumpAhead before the damage window has filled.
`for_sweep` (Pass 1) sets `bisect_on_marginal=false`,
`fast_jump_threshold=4`, and zeroes the post-failure pause. Failed
batches become SkipBlock → whole block NonTrimmed → advance, no
sleep. After 4 consecutive outer failures: JumpAhead with the
existing escalating multiplier.
`for_patch` (Pass N) sets `bisect_on_marginal=true`,
`fast_jump_threshold=u64::MAX`, keeps the original cooldown pauses.
Pass N's whole reason to exist is to grind on bad ranges with
proper recovery semantics — single-sector reads, 60s recovery
timeout, retry budget, escalating skip — and that's unchanged.
`on_success` resets `consecutive_outer_failures` only when not
bisecting, so a good single-sector read inside Pass N's bisect
doesn't pretend we've escaped the damaged batch.
Tests:
- `pass_n_marginal_with_batch_gt_1_bisects` — Pass N still bisects.
- `pass_1_marginal_skips_instead_of_bisecting` — Pass 1 doesn't.
- `pass_1_jumps_after_4_consecutive_outer_failures` — fast-entry.
- `pass_n_does_not_fast_jump` — fast-entry is Pass-1-only.
- `outer_success_resets_consecutive_outer_failures` — counter reset.
- `bisect_inner_success_does_not_reset_outer_counter` — semantics.
- `pass_1_does_not_pause_on_skip` — explicit zero-pause contract.
- `long_failure_streak_extends_pause_on_pass_n` — Pass N still
extends pauses on long failure streaks (renamed from the old
sweep-based test).
Integration test `test_disc_copy_marks_failed_ecc_blocks_as_nontrimmed`
updated: it used to assert Pass 1 recovers all sectors via bisect
(bytes_good=total). New contract: Pass 1 marks NonTrimmed; Pass N
recovers. Test now asserts Pass-1-only outcome (bytes_pending=total,
complete=false) consistent with the redesign.
Real-world impact on the user's BU40N + Dune Pt 2 trace from this
session: a damage zone that was on track to take ~40 minutes of
Pass-1 grinding will now jump in ~20 seconds. Pass N still has the
full 7-pass recovery budget to revisit those NonTrimmed ranges.
matthew
f755ca9ea4