fix: add is_unsupported_shape() guard before rewrite_compound()

[Ev3lynx727]

Summary

Fixes #2902 — which is the root cause of #2792, #2821, #2892.

rewrite_command() attempts to rewrite unsupported command shapes without early validation, producing malformed rtk invocations that fail at runtime.

Changes

Adds is_unsupported_shape() function that returns early before expensive tokenization/regex matching:

• find / fd — excluded entirely because rtk find/rtk fd only support -name, -iname, -type, -maxdepth. Any other predicate (-not, -exec, -newermt, -path, etc.) silently produces wrong/empty results.
• rtk find / rtk fd — already-routed to a subcommand rtk can't rewrite further
• Unattestable constructs — backticks, $((, <( — output shape is unpredictable

User-facing impact

Before this fix, commands like find . -name "*.log" or fd -e rs were rewritten to rtk find ... / rtk fd ..., which either exit with code 3 (ask) or silently produce wrong results when complex predicates are involved.

After this fix, unsupported command shapes pass through to the native command unchanged — no rewrite, no malformed invocation, no silent corruption.

Changelog

- fix: add is_unsupported_shape() guard to skip rewrite for find/fd, already-routed rtk subcommands, and unattestable shell constructs (#2903)
- fix: prevent malformed rtk find/fd invocations from unsupported predicates (#2902, #2792, #2821, #2892)

Verification

• cargo fmt --all — clean
• cargo clippy --all-targets — no new warnings
• cargo test --all — 2399 passed, 0 failed, 8 ignored (baseline)

Related

• Closes Claude Code hook rewrites unsupported command shapes (compound find, multi-file cat) into failing rtk invocations #2792 — Hook rewrites unsupported shapes
• Closes rtk find warns on unknown predicates but then executes a DIFFERENT (broader) query — silent wrong results #2821 — Unknown predicates silently dropped
• Closes RTK hook: find returns empty stdout silently (directory exists with files) — hook should passthrough instead #2892 — find returns empty stdout

[Ev3lynx727]

Thanks for the review @tapheret2 — both nits addressed:

1. User-facing impact — added to PR description (before/after: unsupported shapes now passthrough instead of producing malformed invocations)
2. Changelog — two entries added to PR description, ready for the next release tag

Appreciate the independent pass!

[TheCookieLab]

I reproduced the compound-find failure on v0.44.0 and current develop. A narrower prototype avoids disabling useful simple find rewrites: expose the runtime parser's unsupported-token predicate from find_cmd, have the discovery registry return Ignored only when those tokens are present, and cover both sides (compound/action forms produce no rewrite; find . -name '*.rs' remains rewriteable). The shared predicate also prevents the hook and runtime support lists from drifting. Tested cases include -o, -not, -exec, -delete, -print, and -print0. I can turn that focused prototype into a PR if maintainers prefer selective fallback over skipping every native find/fd command.

[KuSh]

Thank you for tracking this down. The find part was fixed differently in #3603 (merged 2026-08-26): rtk find now follows find's own grammar and hands predicates it does not model to the real find, so find commands can keep being rewritten safely instead of being skipped. The other shapes in this PR are already left alone on develop: fd is not rewritten, an existing rtk find command comes back unchanged, and commands with backticks, $(( or <( are never rewritten. If a case here still misbehaves on the latest version, please comment or reopen with the command.