PR #30478 - manaflow-ai/cmux

Base-red fix (fix forward). The Rust panic ratchet is red on feat-cmux-next since 72dc85db17a (#30361, Cloud repository discovery). The tip watcher's --arg panic step failed at 4cd800a309c2 (job 63b147f0938fdb56741e7c83) and again at b9b4ac567ea8 (job b2e7ab23614482433a9e00b5). It passed at 4b15acdb7ae8 (job 919042f7eb84849e08597ca8).

crate	`clippy::indexing_slicing` at the tip	baseline
acpmux	694	686
cmux-host	1	0
cmux-tui	836	831
cmux-tui-core	880	853

The watcher reported only the first crate (acpmux, +8). Four crates are red. All of the new hits come from #30361. The other first-parent commits in 4b15acdb7ae8..4cd800a309c2 (#30197, #30157, #28937, #30362, #29826 and others) add no index or slice in production code.

What changed

Each serde_json index read that #30361 added in production code is now a get / pointer read. The one IndexMut is now get_mut. The slice command[..2] is now command.get(..2). The baseline is not raised.

file	hits	now
`acpmux/src/cloud_repo_mcp.rs`	17	`get(..).and_then(Value::as_str)`, `pointer("/error/code")`, and `get_mut("error")` in `enrich_retry`
`cmux-host/src/cloud/github_repos.rs`	3	`pointer("/error/code")`, `get("provider")`, `get("_tag")`
`cmux-tui/src/cli/cloud_repo.rs`	4	`get("id")`, `get("ok")`, `get("error_code")`, `get("error")`
`cmux-tui/src/cli.rs`	1	`command.get(..2).is_some_and(..)` (the old code checked `len() >= 2` first)
`cmux-tui-core/src/cloud_repos/{engine,local,runtime,store}.rs`	rest	`get` / `pointer` reads; `store.rs` gets two small readers, `chat_repos` and `recent_repos`

There is no change in behavior. A missing key read through get gives the same result as the Null that indexing returned:

v["k"] == "x" becomes as_str() == Some("x").
v["ok"] != true becomes as_bool() != Some(true).
existing["ref"] != json!(reference) keeps Null for a missing key.
from_value(doc["local"].clone()) becomes from_value(get(..).cloned().unwrap_or_default()), which is still Null, so a missing list still fails the same way.
enrich_retry used to write through &mut result["error"] only when result["error"] was an object, so the get_mut form takes the same branch.

Update after the merge of feat-cmux-next (1dfc4dd6266)

The merge had conflicts in cloud_repo_mcp.rs, engine.rs and runtime.rs with #30528 (let-chains) and #30382 (seed.unknown_job). The resolution keeps their logic and the get reads. At the merge head 9d4a172af476 the ratchet was still red (job 1764d0cc925c9f12951dc4c3) on two rows that later base commits added. Both are fixed here too, because base reds go in one PR:

acpmux indexing_slicing 689 > 686: #30439 added summary["turn"] in hub/views.rs and self.running[at] (twice) in subagents.rs. They are now get("turn") and get_mut(at). at is a position in the same Vec, found just before with no change between.
cmux-tui string_slice 83 > 82: #30464 added &text[prefix.len()..] in link/seed/github.rs. It is now split_at_checked, which gives None in the same cases as the old get(..n).

Testing

run	ref	result
panic ratchet (`--arg panic`)	tip 4cd800a309c2	RED: the four rows above, job 63b147f0938fdb56741e7c83
panic ratchet (`--arg panic`)	first head 8b701f471bc5	pass (exit 0, no RED row, `indexing_slicing` at or under the baseline in all four crates), job 0b990c6938c0c3ba18439332. The warn-tier rows (arithmetic, casts) are the same as on the tip.
`test cloud_repo` (acpmux `cloud_repo_mcp`, cmux-tui-core `cloud_repos`, cmux-tui `cli::cloud_repo` and `cloud_repo_tools`)	8b701f471bc5	37 of 37 pass, job 6083001dc37f62bd46fd723c
`test github_repos` (cmux-host)	8b701f471bc5	9 of 9 pass, job cf655a5395608395acddeb21
panic ratchet (`--arg panic`)	merge head 9d4a172af476	RED: acpmux 689 > 686 and cmux-tui string_slice 83 > 82, from #30439 and #30464, job 1764d0cc925c9f12951dc4c3
panic ratchet (`--arg panic`)	head f9a0611a0188	pass (no RED row), job 1f0e6bb20a1631d3f73a8b30
`test subagents`	f9a0611a0188	51 of 51 pass, job 2d550515957dbd10a47c1254
`test seed`	f9a0611a0188	79 of 79 pass, job 9fac88983e527560cdbb0f29
`test cloud_repo`	f9a0611a0188	37 of 37 pass, job 5d73878f27ac96fcd368f66b

Review (subagent, correctness first): SHIP at 8b701f471bc59e073c3a2ad36fda79ed7e2008ac, at 9d4a172af4763b798d5ac2606d992edf46356ff3 (the merge) and at f9a0611a018858eff511ddd69a96884745836e80 (the current head). It checked every rewrite against serde_json semantics and the enrich_retry borrow and found no blocking issue.

Observed / Not run

Observed: all the runs above (fleet Linux, Blacksmith overflow), prepush-gate.py (no new violations), and rustfmt 1.95 on the changed files.
Not run: macOS builds, because this PR has no Swift change. I did not run a macOS clippy, because the panic ratchet runs on Linux. #30555 (cloud_repo.rs validate is_none_or) overlaps 4 let-chain sites; whichever lands second merges the other.

Changelog

none