docs(limitations): add explicit boundaries guide

[ded-furby]

Fixes #117.

Summary

• add a root LIMITATIONS.md that states Talon's current non-claims in plain language
• cover the boundaries called out in the issue: sandboxing, trust mesh scope, tool governance maturity, HMAC signature semantics, compliance responsibility, and key-management assumptions
• link the new guide from the top of README.md

Validation

• npx --yes markdown-link-check@3.12.2 README.md LIMITATIONS.md -c .github/mlc_config.json
• make check could not complete in this environment because golangci-lint is not installed locally (make: golangci-lint: No such file or directory)

[sergeyenin]

Hi @ded-furby , thank you for your contribution. Would you like to make the documentation more precise and consice ?

[ded-furby]

Pushed a follow-up revision to tighten . I shortened the intro, removed repeated phrasing, and made each boundary statement more specific around request-path scope, tool filtering, HMAC semantics, and operator responsibility.

[ded-furby]

Pushed a follow-up revision to tighten LIMITATIONS.md. I shortened the intro, removed repeated phrasing, and made each boundary statement more specific around request-path scope, tool filtering, HMAC semantics, and operator responsibility.

[sergeyenin]

Thanks, @ded-furby — and sorry for the overlap. A LIMITATIONS.md has since landed on main, so this PR doesn't apply cleanly anymore. That said, two of your points are sharper than what's there, and it would be great to see them land as your contribution:

• Talon does not prevent the same tool from being invoked on a path that does not pass through Talon.
• Folding the signing-key-custody assumption into the HMAC claim ("…assuming the signing key remains protected").

If you'd be interested, the simplest path is probably to rebase onto main and add those two thoughts to the existing Tool-governance and Evidence sections — but no pressure at all, and I'm happy to help if it's useful. Either way, thank you — you'll be credited.

[ded-furby]

I applied the requested follow-up locally on top of current main, but I could not push the rebased branch from this environment because the GitHub token here does not have workflow scope and GitHub rejected the ref update while the branch history crossed .github/workflows/ci.yml changes.

The exact LIMITATIONS.md changes on top of current main are:

• In Tool-governance boundary: Talon does not prevent the same tool from being invoked on a separate path that does not pass through Talon.
• In Evidence boundary: extend the signature sentence to end with assuming the signing key remains protected.

I re-ran npx --yes markdown-link-check@3.12.2 LIMITATIONS.md -c .github/mlc_config.json successfully against that current-main version. make check still stops early here because golangci-lint is not installed in this environment (make: golangci-lint: No such file or directory).