MSC4352 (unstable): discover org.matrix.msc4352.permalink_base_url; share via :permalink; linkify resolver HTTPS to matrix: on send

[DonPrus]

This PR adds an experimental client-side implementation for MSC4352 to help it move through the spec process. It demonstrates:

1. Discovery: Reads org.matrix.msc4352.permalink_base_url (or stable m.permalink_base_url) from /.well-known/matrix/client for the user's homeserver domain (HTTPS-only). Also supports IAMB_MSC4352_PERMALINK_BASE for local testing.

2. Generation: New command :permalink generates HTTPS permalinks for outside-of-Matrix contexts using the matrix.to navigation grammar but with the discovered custom base URL (fallback https://matrix.to). Supports both room permalinks and event permalinks (:permalink event $eventId).

3. In-app safety: No in-app links/mentions are rewritten to HTTPS; iamb's in-app navigation remains intact.

4. Send-time conversion: When a user pastes a resolver-style HTTPS permalink in a message, iamb keeps the visible text but emits formatted_body with an equivalent matrix: URI (matrix:r/..., matrix:roomid/.../e/..., preserving via=), ensuring cross-client interoperability.

Feature flag

Set IAMB_MSC4352=1 to enable the feature. You can optionally set IAMB_MSC4352_PERMALINK_BASE for testing without editing well-known.

Testing

• Send conversion: Paste https://links.example.org/#/%23room%3Aexample.org/%24event?via=example.org and send - the message should have an anchor with href="matrix:r/room:example.org/e/$event?via=example.org" in formatted_body, while body preserves the original text.
• Permalink generation: Run :permalink in a room to get an HTTPS permalink based on discovered or env-provided base.
• Fallback: Without well-known and without the env var, :permalink falls back to https://matrix.to.

Implementation notes

• Prefers canonical room alias over room ID when generating permalinks
• Validates HTTPS-only for discovered base URLs
• Includes comprehensive unit tests
• Documented in MSC4352.md

This is intentionally a small, low-risk change to qualify MSC4352 with a client implementation.

[VAWVAW]

Is there a reason this PR needs to reimplement existing types like MatrixID, MatrixUri and MatrixToUri?

I think it makes more sense to implement most of this in matrix-rust-sdk and maybe just do a string replace in the output of MatrixToUri::to_string.

Also I couldn't get this to build (unresolved import url::percent_encoding and modalkit::clipboard) but this looks like it breaks markdown formatting in messages with matrix.to links.

[DonPrus]

Is there a reason this PR needs to reimplement existing types like MatrixID, MatrixUri and MatrixToUri?

I think it makes more sense to implement most of this in matrix-rust-sdk and maybe just do a string replace in the output of MatrixToUri::to_string.

Also I couldn't get this to build (unresolved import url::percent_encoding and modalkit::clipboard) but this looks like it breaks markdown formatting in messages with matrix.to links.

Thanks, I fix this:

• Use existing ruma types (MatrixUri, MatrixToUri) instead of reimplementing them
• Fix the import issues with percent_encoding
• Preserve markdown formatting by applying MSC4352 conversion after markdown processing
• Simplify the code by leveraging existing matrix-sdk functionality

[VAWVAW]

Do you have some local changes you have not pushed or are you using AI to write this code? When I check out your changes locally and run cargo c, I get multiple error about non-existing functions and attributes.

[DonPrus]

Apologies for the confusion. The issue is that main doesn’t build for me on macOS 26. To get a local build, I’ve been temporarily tweaking build.rs and a few other files, and adding some helper/stub files to work around platform-specific errors. I didn’t commit those local changes, which is why a clean checkout hits the “non-existing functions/attributes” errors you’re seeing. I’ll sort out my macOS setup closer to the weekend, push the minimal required changes (or guard the macOS-specific bits), and re-test with a clean cargo c run.

[VAWVAW]

For me 28acbaa complies while 1d266fd complains about modalkit::clipboard not existing.

[DonPrus]

Now I fix all problems, and add some more tests for this feature :)