AMBIGUOUS_MATCH and unsupported find actions give agents nothing to recover with

[thymikee]

Ambiguous rejection is by-design and stays. But the error carries no candidates, so driving agents burn their budget guessing:

Error (AMBIGUOUS_MATCH): find matched 4 elements for any "Members". Use a more specific locator or selector.

Benchmarked cost (AppControlBench): element-13 (gpt_high) oscillated for 83 tool calls and never recovered; element-29 and bsky-16 hit the same wall, and both then tried find "#caturday" press / find "Members" press, getting:

Error (INVALID_ARGS): Unsupported find action: press

with no pointer to the correct two-step.

Proposed:

1. AMBIGUOUS_MATCH lists the matching candidates (ref, role, label/identifier — capped at ~5, same rendering as snapshot lines) so disambiguation is one step: pick the @ref and act on it.
2. find <text> <unsupported-action> names the supported find actions AND hints the recovery shape: find "Members" to list matches, then press @eNN.

Both are error-payload/hint changes only; matching semantics unchanged.