fix(cli): report correct error when sharding without a fullHandle

What changed

Running a sharded test execution on a project that has no fullHandle now fails with a message that names the real problem instead of a misleading one about flag conflicts.

Before:

✖ Error
  Cannot specify both --build-only and --without-building

After:

✖ Error
  Test sharding requires a Tuist account. The 'Tuist.swift' file is missing a fullHandle. See how to set up a Tuist project at: https://tuist.dev/en/docs/guides/server/accounts-and-projects#projects

Why

A user reported that tuist test --without-building --shard-index 0 instantly failed with Cannot specify both --build-only and --without-building, even though neither flag combination was used.

Root cause

That message belongs to the actionInvalid error, which is correctly raised in command validation only when --without-building and --build-only are genuinely combined. The problem was that runShard reused the same actionInvalid case for an unrelated condition: the project has no fullHandle, i.e. it isn’t connected to the Tuist backend. Sharding is server-backed, so without a fullHandle it bails out — but it surfaced an error about flags that were never combined.

Why this fix

Rather than overloading actionInvalid for two unrelated conditions, this adds a dedicated shardingRequiresFullHandle error whose message points at the actual cause and links to the project setup docs (matching the phrasing already used by other fullHandle-missing errors in the CLI). actionInvalid keeps its original, correct meaning for the real --without-building + --build-only conflict.

Impact

Users attempting test sharding on a non-connected project now get an actionable error instead of a confusing one. No behavior change for connected projects or for the genuine flag-conflict case.

Validation

• Added test_throws_when_shard_index_is_passed_without_full_handle, which pins that a --shard-index run on a config with fullHandle: nil throws shardingRequiresFullHandle.
• The CLI test target can’t be executed in this environment (no PTY for xcodebuild test); the change is otherwise verified by inspection against the existing shard-validation test patterns.

🤖 Generated with Claude Code