[lawrencecchen]

Summary

Culprit: #30726 (fbaa7a5, Leo), "feat(acpmux): byte-bound background-process history with opt-in pages (SW-11)". It added ten clippy::indexing_slicing hits in cmux-tui/crates/acpmux/src/hub/processes.rs:

• self.processes[start..end] in ProcessTable::page_snapshot (line 327).
• Nine serde_json indexes row["..."] in the too-large row of process_page_values (lines 384-388).

The Rust panic ratchet is red on feat-cmux-next: acpmux 697 > baseline 686 at 7da73fe (hq run 41384159581), and 696 after #31695 removed the #30712 hit. The broken Cargo.lock from #31462 hid this red until #31717.

This PR:

• reads the window with self.processes.get(start..end).unwrap_or_default(). start is an ID's slot + 1 (at most len) or 0, and end = min(start + limit, len), so the range is always in bounds and the fallback never applies.
• reads the row fields with row.get(..). An Option<&Value> serializes None as null, the same as an index on a missing key, so the reply does not change.

It also fixes one more hit that came on the tip after #31695: #31709 (030cb46, Leo, "Settings > Retry After Errors sets acpmux's retry loop") added DEFAULT_DELAYS_MS[n.min(DEFAULT_DELAYS_MS.len() - 1)] in hub/auto_resume/settings.rs. It now reads DEFAULT_DELAYS_MS.get(n).or(DEFAULT_DELAYS_MS.last()): past the defaults the last wait repeats, as before. The array is a non-empty const ([u64; 4]), so the MIN_DELAY_MS fallback never applies.

No baseline change and no allow.

Testing

Focused command (fleet, Linux route): cmux-ci run --class light --script scripts/ci/cmux-tui-rust-check.sh --arg panic --os linux --ref <sha>.

• Tip 8fad072aafc (with base red: acpmux lose_running reads its slot without an index (panic ratchet indexing_slicing 687 > 686, #30712) #31695): RED, acpmux: clippy::indexing_slicing 697 > baseline 686 (job 4fbbc710c433f636164a8524, hq run 41388454113).
• Earlier head 2f95be6b0cf (only the feat(acpmux): byte-bound background-process history with opt-in pages (SW-11) #30726 fix): still RED, 687 > 686; the extra hit is cmux NEXT: Settings > Retry After Errors sets the automatic retry loop (on/off, seconds between tries, tries per error) #31709's (job e04b07004910adff2b197d6e, hq run 41386195677).
• Head d561fd27997: green, rust-panic-ratchet: 80 crates checked, 30 at deny (job 2b80c682d0c03462ac781c8a, hq run 41388454076).
• acpmux process tests (--arg test --arg process_) at the head: 145 passed (job fe6209efcdec5c0b9e069f4b, hq run 41388453748).
• acpmux retry tests (--arg test --arg auto_resume) at the head: 101 passed (job 5cfaee5e3c404f45cda447d0, hq run 41388454078).

Observed / Not run

• Observed: the fleet logs above. prepush-gate.py: no new violations. rustfmt --check on the file: clean.
• Not run: no local cargo build, clippy or test (fleet only). I did not drive _acpmux/process/list pages or the retry settings by hand.

Changelog

none

Related: #31697 (Linux clippy fix for #31462's plugin_manager.rs). The two fixes are independent: each step fails on its own, and neither step needs the other fix to run.

[github-actions]

cmux status _{(one comment, edited in place; each line is updated by the job that owns it)}

Review d561fd2: HQ feed card · gallery before/after runs · checks

App of this head (app.zip, kept 1 day)

gh workflow run reload-build.yml -R manaflow-ai/cmux --ref feat-cmux-next -f tag=pr31773 -f ref=base-red/acpmux-process-pages-index -f platform=macos -f backend_mode=local

web and size checks: green

Shipped in:

• cmux NEXT nightly 1.0.0-nightly.4139510839501 (d47dcbddc6)
• cmux NEXT nightly 1.0.0-nightly.4139567428201 (14a5e1b153)
• cmux NEXT nightly 1.0.0-nightly.4139686277401 (4e9b96d7dd)
• cmux NEXT nightly 1.0.0-nightly.4139750725501 (947bb5e00d)

[blacksmith-sh]

Found 4 test failures on Blacksmith runners:

Failures

Test	View Logs
main.DeveloperIdAppTests.test_download_prints_the_active_profile_only/ test_download_prints_the_active_profile_only	View Logs
stubs: /System/Library/Frameworks/Security.framework/Versions/A/Security has no stub/ Security has no stub	View Logs
stubs: CoreFoundation.tbd: install-name /System/Library/Frameworks/ CoreFoundation.framework/Versions/A/CoreFoundation, missing 1: ['_CFRetain']/ CoreFoundation, missing 1: ['_CFRetain']	View Logs
stubs: CoreFoundation.tbd: install-name /System/Library/Frameworks/ CoreFoundation.framework/Versions/A/CoreFoundation, missing 1: ['_log2']/ CoreFoundation, missing 1: ['_log2']	View Logs

^{Need help on this PR? Tag @codesmith-bot with what you need.}

[lawrencecchen]

Review (subagent, correctness first): SHIP at d561fd2

Checked (net diff against origin/feat-cmux-next, 2 files, +15/-7):

• ProcessTable::page_snapshot: by_id is written only in insert, which stores at = processes.len() and then pushes. No code removes, truncates or reorders processes. upsert replaces a slot in place. read_processes / rebuild_processes replace the whole table, so by_id and processes always change together. So every by_id value is < len, start <= len, and start <= end = min(start + limit, len) <= len. get(start..end) is always Some, and the reply is the same as before. If the invariant ever broke, the old code panicked and the new code returns an empty page. That is no change for any reply the old code could send. unwrap_or_default() on Option<&[Process]> uses Default for &[T].
• process_page_values stub: json! serializes each value through to_value(&expr). Option<&Value> gives Null for None and a clone of the value for Some, and Value's Index gives &Null for a missing key. So the output is the same. The macro builds the new Value from borrows of row and then assigns it, the same as the index form did. one_oversized_command_yields_a_stop_capable_stub covers this path.
• settings_delays: DEFAULT_DELAYS_MS: [u64; 4] (auto_resume.rs:123). For n < 4, get(n) is arr[n]. For n >= 4, .or(last()) is arr[3], which is arr[n.min(3)]. The MIN_DELAY_MS fallback cannot run. This also removes one arithmetic_side_effects hit (len() - 1): acpmux 1488 -> 1487 in the logs.
• The comments are accurate. rustfmt --check --edition 2024 --config-path cmux-tui/rustfmt.toml passes on both files.
• Fleet logs: run 41388454113 at 8fad072 shows acpmux: clippy::indexing_slicing 697 > baseline 686, exit 1. Run 41388454076 at d561fd2 passes with no indexing_slicing line. Runs 41388453748 (process_: 145 passed) and 41388454078 (auto_resume: 101 passed) both checked out d561fd2.
• The PR description matches the code. There is no baseline change and no allow.