fix(cli): fresh path keeps auto -> anyrouter/auto for first-turn failover (#58)

[duyetbot]

Fresh (no --model) now leaves ANYROUTER_MODEL_MODE=auto and ANTHROPIC_MODEL=anyrouter/auto on a fresh install, instead of pinning the most-used single catalog model. Pinning a single model disables anyrouter/auto's health-aware cross-model failover chain.

• src/cmd/launch.rs: keep auto/anyrouter/auto as-is through resolve_session_model; the /models lookup still supplies the context-window probe for Claude's 1M suffix.
• src/help.rs: document the default model behavior.
• most_used_model_id retained for the models-list UI.

Dry-run on a fresh home (with a valid key) now emits:
ANYROUTER_MODEL_MODE=auto
ANTHROPIC_MODEL=anyrouter/auto
CLAUDE_CODE_ENABLE_GATEWAY_MODEL_DISCOVERY=1

Companion anyrouter PR: #3154 (caugiay disable + auto head bias to stable flagships).

[github-actions]

anyr size and startup

Startup is wall time for a cold anyr --version / anyr --help (median of 21 runs). Size is the stripped release binary, or the .wasm for the browser demo.

Size budget: anyr-linux-x86_64 must stay ≤ 4.0 MiB (4194304 bytes) stripped.

Asset	Kind	Size	--version median	--help median
anyr-darwin-arm64	native	2.8 MiB	3.66 ms	3.05 ms
anyr-darwin-x86_64	native	3.0 MiB	34.21 ms	37.91 ms
anyr-linux-arm64	native	2.8 MiB	0.71 ms	0.7 ms
anyr-linux-x86_64	native	3.1 MiB	0.97 ms	0.95 ms
anyr-windows-x86_64.exe	native	2.6 MiB	8.64 ms	8.77 ms
anyr.wasm	wasm	176.2 KiB	—	—

Budget check: ok

raw timings

[
  {
    "asset": "anyr-darwin-arm64",
    "kind": "native",
    "path": "/Users/runner/work/cli/cli/anyr-darwin-arm64",
    "bytes": 2927800,
    "size": "2.8 MiB",
    "version": "0.1.11 (built 2026-09-06 15:19:27)",
    "target": "aarch64-apple-darwin",
    "os": "macos-latest",
    "startup_version": {
      "n": 21,
      "min_ms": 3.43,
      "median_ms": 3.66,
      "p95_ms": 5.6,
      "mean_ms": 4.06
    },
    "startup_help": {
      "n": 21,
      "min_ms": 2.88,
      "median_ms": 3.05,
      "p95_ms": 3.83,
      "mean_ms": 3.18
    }
  },
  {
    "asset": "anyr-darwin-x86_64",
    "kind": "native",
    "path": "/Users/runner/work/cli/cli/anyr-darwin-x86_64",
    "bytes": 3133720,
    "size": "3.0 MiB",
    "version": "0.1.11 (built 2026-09-06 15:18:38)",
    "target": "x86_64-apple-darwin",
    "os": "macos-latest",
    "startup_version": {
      "n": 21,
      "min_ms": 30.92,
      "median_ms": 34.21,
      "p95_ms": 38.73,
      "mean_ms": 34.68
    },
    "startup_help": {
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      "median_ms": 37.91,
      "p95_ms": 68.38,
      "mean_ms": 41.21
    }
  },
  {
    "asset": "anyr-linux-arm64",
    "kind": "native",
    "path": "/home/runner/work/cli/cli/anyr-linux-arm64",
    "bytes": 2888744,
    "size": "2.8 MiB",
    "version": "0.1.11 (built 2026-09-06 15:18:16)",
    "target": "aarch64-unknown-linux-gnu",
    "os": "ubuntu-24.04-arm",
    "startup_version": {
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      "min_ms": 0.65,
      "median_ms": 0.71,
      "p95_ms": 0.76,
      "mean_ms": 0.71
    },
    "startup_help": {
      "n": 21,
      "min_ms": 0.67,
      "median_ms": 0.7,
      "p95_ms": 0.78,
      "mean_ms": 0.71
    }
  },
  {
    "asset": "anyr-linux-x86_64",
    "kind": "native",
    "path": "/home/runner/work/cli/cli/anyr-linux-x86_64",
    "bytes": 3230264,
    "size": "3.1 MiB",
    "version": "0.1.11 (built 2026-09-06 15:18:31)",
    "target": "x86_64-unknown-linux-gnu",
    "os": "ubuntu-latest",
    "startup_version": {
      "n": 21,
      "min_ms": 0.95,
      "median_ms": 0.97,
      "p95_ms": 1.02,
      "mean_ms": 0.98
    },
    "startup_help": {
      "n": 21,
      "min_ms": 0.92,
      "median_ms": 0.95,
      "p95_ms": 1.11,
      "mean_ms": 0.97
    }
  },
  {
    "asset": "anyr-windows-x86_64.exe",
    "kind": "native",
    "path": "D:\\a\\cli\\cli\\anyr-windows-x86_64.exe",
    "bytes": 2674688,
    "size": "2.6 MiB",
    "version": "0.1.11 (built 2026-09-06T15:19:43Z)",
    "target": "x86_64-pc-windows-msvc",
    "os": "windows-latest",
    "startup_version": {
      "n": 21,
      "min_ms": 8.48,
      "median_ms": 8.64,
      "p95_ms": 9.19,
      "mean_ms": 8.73
    },
    "startup_help": {
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      "median_ms": 8.77,
      "p95_ms": 9.17,
      "mean_ms": 8.86
    }
  },
  {
    "asset": "anyr.wasm",
    "kind": "wasm",
    "path": "/home/runner/work/cli/cli/target/wasm-pkg/anyr_cli_bg.wasm",
    "bytes": 180433,
    "size": "176.2 KiB",
    "version": "wasm",
    "target": "wasm32-unknown-unknown",
    "os": ""
  }
]