fix(cosh-ng): swap remaining chunks_exact uses

[jfeng18]

Why

Clippy 1.98 (rolling stable) ships the new chunks_exact_to_as_chunks lint. Beyond the decode_hex site fixed in #2742, the same lint fires on two more chunks_exact(2) sites. This PR delivers the follow-up promised in the #2742 review discussion (KaiLongZhou's non-blocking observations).

What changed

Swapped .chunks_exact(2) for .as_chunks::<2>().0.iter() (the exact form clippy suggests) in:

• cosh-core/src/tool/grep.rs — decode_utf16_bytes: both forms iterate full 2-byte units and drop the tail remainder; the odd tail is handled separately via has_partial_unit, unchanged.
• cosh-shell/src/recommendation/personal_crypto.rs — test-only decode_hex helper; std::str::from_utf8(pair) accepts the &[u8; 2] items via unsize coercion.

Note on the other half of the promised follow-up: the MSRV alignment (observation 1) is already done — 77c4e8b ("feat(cosh-ng): [gateway] add ACP v1 foundation") set rust-version = "1.88" on main, matching the 1.88.0 pinned CI jobs, so no Cargo.toml change is needed here.

Related issue

no-issue: pre-existing code flagged by a new clippy lint, not a user-visible bug. Attribution per repo convention in the commit body: Fixes: c818e11876a3 ("fix(cosh-ng): [core] confine read tools") and Fixes: 8d4d74c12e70 ("feat(cosh-ng): add shell prompt recommendations").

User / Agent impact

None. Semantics-preserving internal refactor; no public API, CLI, or behavior change.

Risk and compatibility

• Public CLI, API, configuration, or documented behavior changed
• Privileged or security-sensitive behavior changed
• Cross-component contract changed
• Migration or rollback guidance is needed

Low risk: as_chunks stabilized in Rust 1.88; cosh-ng CI pins 1.88.0 (integration/release-build) and 1.97.1 (fast checks) — neither toolchain carries this lint, so the pinned jobs compile and lint unchanged.

Validation

• Discriminating lint evidence (ECS Linux, stable 1.98 clippy, -p cosh-core -p cosh-shell --all-targets --keep-going):
  • pre-fix on the main baseline (with query.rs temporarily mirroring the fix(cosh-ng): swap chunks_exact for as_chunks #2742 patch so cosh-platform compiles and cosh-core gets reached): the lint fires at grep.rs:511 and personal_crypto.rs:259
  • post-fix (this PR): both target sites disappear from the lint output; exit code still non-zero only because of the out-of-scope sites below
• ECS, RUSTUP_TOOLCHAIN=1.89.0: cargo clippy -p cosh-core -p cosh-shell --all-targets -- -D warnings — exit 0
• ECS, RUSTUP_TOOLCHAIN=1.88.0: cargo check -p cosh-core -p cosh-shell — exit 0 (MSRV floor confirmed; the two pre-existing fs2 unlock() future-incompat warnings in extension/ are unrelated to this change)
• ECS, 1.89.0: cargo test -p cosh-core --lib — 124 passed / 0 failed; cargo test -p cosh-shell --lib — 1347 passed / 0 failed
• Local cargo fmt --all -- --check with both 1.89.0 and stable 1.98 — clean
• Known out-of-scope remainder: personal_crypto.rs:66 (SHA256_BLOCK_BYTES) and :172 (chunks_exact(4)) also trip the same lint on clippy 1.98; they are not the chunks_exact(2) sites called out in the review and the pinned CI toolchains do not carry the lint. Left for a later pass if fast checks ever move to a lint-carrying toolchain (same for query.rs, owned by fix(cosh-ng): swap chunks_exact for as_chunks #2742).

Documentation and rollback

None. Revert the single commit to restore the previous form.

[qoderai]

本次修改主要是将若干 chunks_exact(2) 换成 as_chunks::<2>().0.iter() 以满足新 clippy lint 要求，作用范围仅在 cosh-core 和 cosh-shell 内部，不涉及对外行为。

我重点核对了：

• decode_utf16_bytes / decode_hex 对奇数字节尾部的处理是否保持一致；
• PR 描述与实际 diff 是否完全一致，避免遗漏 chunks_exact(2) 站点；
• MSRV 及 clippy lint 行为与使用的 as_chunks 写法是否兼容。

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[KaiLongZhou]

Code Review — PR #2756

结论：LGTM ✅ — 未发现阻塞问题

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语义等价性验证

Site 1 — cosh-core/src/tool/grep.rs:511 (decode_utf16_bytes)

	chunks_exact(2)	as_chunks::<2>().0.iter()
Iterator item	&[u8] (len=2)	&[u8; 2]
Closure 中 bytes[0], bytes[1]	✅ 正常工作	✅ 正常工作
尾部余量处理	丢弃，由 has_partial_unit 处理	相同 — .0 同样丢弃余量

语义完全等价。read_utf16_unit 接收 [u8; 2] 值类型，两种情况下 [bytes[0], bytes[1]] 构造结果一致。

Site 2 — cosh-shell/src/recommendation/personal_crypto.rs:259 (test decode_hex)

	chunks_exact(2)	as_chunks::<2>().0.iter()
Iterator item	&[u8] (len=2)	&[u8; 2]
from_utf8(pair)	&[u8] → 直接匹配	&[u8; 2] → unsize coercion 到 &[u8]

语义完全等价。std::str::from_utf8 签名接受 &[u8]，&[u8; 2] 通过 unsized coercion 自动转换。

MSRV 兼容性

as_chunks::<N>() 在 Rust 1.88 稳定。当前 rust-version = "1.88" (77c4e8b)，CI pinned 1.88.0 / 1.97.1 — 兼容无问题。

Out-of-scope 站点

PR 描述正确记录了以下已知未修复的 chunks_exact 站点：

• personal_crypto.rs:66 — chunks_exact(SHA256_BLOCK_BYTES)
• personal_crypto.rs:172 — chunks_exact(4)
• query.rs:629 — chunks_exact(2) (由 fix(cosh-ng): swap chunks_exact for as_chunks #2742 负责)

这些不是本 PR 的范围，且当前 CI pinned toolchains 不携带该 lint。

P0 / P1 未发现

变更最小化、目标明确、语义等价，测试覆盖充分（cosh-core 124 passed, cosh-shell 1347 passed）。

[KaiLongZhou]

code-reviewer-check: 审核通过 ✅

已回读 pr-2756 分支代码，逐条验证 code-reviewer 的 review 结论：

1. grep.rs 语义等价 ✅ — as_chunks::<2>().0.iter() 产出 &[u8; 2]，[bytes[0], bytes[1]] 构造 [u8; 2] 传入 read_utf16_unit，类型匹配正确
2. personal_crypto.rs 语义等价 ✅ — from_utf8(pair) 通过 unsize coercion 接受 &[u8; 2]
3. 尾部余量处理不变 ✅ — as_chunks 的 .0 丢弃余量，与原 chunks_exact(2) 行为一致
4. MSRV 兼容 ✅ — as_chunks stabilized in 1.88，匹配 rust-version = "1.88"
5. Out-of-scope 站点记录准确 ✅

未发现遗漏或误判，建议合并。

[KaiLongZhou]

Review Check: LGTM ✅

code-reviewer 的 review 结论经逐项代码回读验证，全部正确：

• 语义等价性：chunks_exact(2) → as_chunks::<2>().0.iter() 两处替换均为语义保持的等价变换（&[u8] → &[u8; 2]，索引行为和 unsized coercion 均兼容）
• MSRV：as_chunks 稳定于 Rust 1.88.0，与 rust-version = "1.88" 匹配
• 范围完整性：cosg-ng 中所有 chunks_exact 调用点已核实，本 PR 覆盖全部 chunks_exact(2) 站点
• Commit 质量：单 commit，+6/-2，diff 最小化，归因完备

结论：可以合并，无阻塞问题。

[KaiLongZhou]

LGTM — review check passed. Semantic equivalence, MSRV compatibility, scope completeness, and commit quality all verified against source code.