fix(desktop): canonicalize stray --acp flag to the acp subcommand for kimi harnesses (#4106)

[iroiro147]

Summary

• normalize_agent_args now canonicalizes the --acp / -acp flag form (case-insensitive) to the bare acp subcommand before args reach the spawn/readiness/config-hash/model-probe paths. Subcommand-style ACP CLIs — Kimi Code, Oh My Pi, OpenCode, Devin, cursor-agent — exit immediately on the flag form with error: unknown option '--acp', so every affected agent failed to start.
• The reporter's environment shows a harness definition whose Arguments field contains --acp (persisted state / manual entry): the Kimi preset itself already ships args: &["acp"] and hint text (kimi acp) on main, so this fixes the flag form at the single shared normalization seam instead of chasing each persisted definition.
• Flag-style harnesses are unchanged: codex-acp / claude-* / buzz-agent still strip the ACP arg to empty via the existing rule, and no flag-style ACP CLI accepts a literal --acp, so this is a pure repair. Non-acp args pass through untouched.

Root cause

normalize_agentargs trimmed and filtered args but passed a literal --acp straight through to the spawned command (BUZZ_ACP_AGENT_ARGS → buzz-acp clap value_delimiter=','). Modern Kimi CLI parses it as an unknown option and exits, so buzz-acp reports "agent process exited unexpectedly / all N agents failed to start".

Changes

• desktop/src-tauri/src/managed_agents/discovery.rs: --acp/-acp → acp canonicalization inside normalize_agent_args (case-insensitive), with a comment explaining the repair.
• desktop/src-tauri/src/managed_agents/discovery/tests.rs:98-139: new canonicalizes_stray_acp_flag_to_subcommand regression test covering bare kimi, path-form .../bin/kimi, opencode, case-insensitivity, multi-arg preservation, correct-form passthrough, codex-acp strip-to-empty, and non-acp flag passthrough.

Verification

• cargo test --lib canonicalizes_stray_acp_flag_to_subcommand — pass.
• cargo test --lib normalize — 26 passed, 0 failed (includes existing agent-args tests).
• cargo test --lib discovery — 245 passed, 0 failed.
• cargo test --lib readiness — 56 passed, 0 failed.
• pnpm typecheck — clean.

Fixes #4106

[iroiro147]

Follow-up on #4113 — the fix was hardened beyond the flag canonicalization:

• default_agent_args now has a kimi arm returning ["acp"] (same fallback pattern as goose), so even a harness definition or agent instance with completely empty args still launches kimi acp. Explicit non-empty instance args still win.
• The --acp/-acp → acp canonicalization now also covers the path-form command (~/.kimi-code/bin/kimi) and is case-insensitive (--ACP).
• Tests: canonicalizes_stray_acp_flag_to_subcommand (8 assertions incl. path-form, case-insensitivity, multi-arg preservation, codex-acp strip-to-empty) plus kimi_default_args_fallback_covers_empty_args (empty/whitespace args → ["acp"], explicit args still win). Full cargo test --lib discovery 245 pass / readiness 56 pass / normalize 26 pass / pnpm typecheck clean.