feat(desktop): share Projects entities by copying a direct link

Projects, repositories, issues, and pull requests had no shareable
reference — the only way to point someone at one was to describe it.
Each now offers "Copy link" in its row menu (plus a copy button in the
project, issue, and pull request detail headers), yielding a `buzz://`
deep link that renders as a preview card in chat and opens the entity
in-app when clicked or opened from the OS.

Completes the entity-link format for this: adds the `buzz://project`
scheme on both sides (TS builders/parser and the buzz-cli mirror, with
`projects create` emitting `link`), resolves repository and project card
titles from their announcement events, and registers the four entity
hosts with the Tauri deep-link handler.

Coordinates whose d-tag falls outside the link charset simply have no
share affordance, rather than producing a link the recipient cannot
parse.

Signed-off-by: Thomas Petersen <thomasp@squareup.com>

crates/buzz-cli/src/commands/projects.rs

@@ -108,13 +108,29 @@ fn make_tag(parts: &[&str]) -> Result<Tag, CliError> {
 
 // ── Submit helper ─────────────────────────────────────────────────────────────
 
-async fn submit_project(client: &BuzzClient, builder: EventBuilder) -> Result<(), CliError> {
+/// Submit a project event and print the relay's write response.
+///
+/// `link_slug` carries the project's d-tag on creates whose slug fits the
+/// `buzz://` link charset; the response then also carries a `link` field,
+/// which renders as a rich preview card in Buzz Desktop when included in a
+/// chat message — agents announce projects with it (see base_prompt.md).
+async fn submit_project(
+    client: &BuzzClient,
+    builder: EventBuilder,
+    link_slug: Option<&str>,
+) -> Result<(), CliError> {
     let event = client.sign_event(builder)?;
+    let owner = event.pubkey.to_hex();
     let raw = client.submit_event(event).await?;
-    println!(
-        "{}",
-        parse_write_response(&raw, "project changed concurrently; retry")?
-    );
+    let response = parse_write_response(&raw, "project changed concurrently; retry")?;
+    match link_slug {
+        Some(slug) => crate::client::print_create_response(
+            &response,
+            "link",
+            &crate::links::project_link(&owner, slug),
+        ),
+        None => println!("{response}"),
+    }
     Ok(())
 }
 
@@ -207,7 +223,15 @@ pub async fn cmd_create(
     // ── Build via Layer B (enforces all writer policy) ────────────────────
     let builder = build_project(slug, name, description, &members, channel, visibility)
         .map_err(|e| CliError::Usage(e.to_string()))?;
-    submit_project(client, builder).await
+
+    // Slugs wider than the link charset stay linkless rather than emitting a
+    // `link` no client can parse.
+    submit_project(
+        client,
+        builder,
+        crate::links::is_linkable_dtag(slug).then_some(slug),
+    )
+    .await
 }
 
 /// `buzz projects get`
@@ -320,7 +344,7 @@ pub async fn cmd_add_repo(
     }
 
     let builder = rebuild_project(&head.content, tags, next_ts)?;
-    submit_project(client, builder).await
+    submit_project(client, builder, None).await
 }
 
 /// `buzz projects remove-repo`
@@ -383,7 +407,7 @@ pub async fn cmd_remove_repo(
 
     // Single rebuild validates the full envelope and strips any remaining auth.
     let builder = rebuild_project(&head.content, tags, next_ts)?;
-    submit_project(client, builder).await
+    submit_project(client, builder, None).await
 }
 
 /// `buzz projects update`
@@ -484,7 +508,7 @@ pub async fn cmd_update(
     let builder = build_project_with_tags(&head.content, tags)
         .map_err(|e| CliError::Other(format!("envelope validation failed: {e}")))?
         .custom_created_at(next_ts);
-    submit_project(client, builder).await
+    submit_project(client, builder, None).await
 }
 
 /// `buzz projects delete`

crates/buzz-cli/src/links.rs

@@ -9,11 +9,34 @@
 //! Callers are expected to validate inputs first (`validate_hex64`,
 //! `validate_repo_id`); the identifier charsets need no URL encoding.
 
+/// Whether a d-tag can be expressed in a `buzz://` link.
+///
+/// Project slugs accept up to 1024 bytes of arbitrary UTF-8, but the link
+/// format is restricted to `[a-zA-Z0-9._-]{1,64}` (no leading dot, no `..`)
+/// so links need no escaping and stay safe to paste. Callers must check
+/// before building a link and omit the field when it returns false, rather
+/// than emitting a link no client can parse. Mirrors `isValidDtag` in
+/// `desktop/src/shared/lib/entityLink.ts`.
+pub fn is_linkable_dtag(dtag: &str) -> bool {
+    !dtag.is_empty()
+        && dtag.len() <= 64
+        && !dtag.starts_with('.')
+        && !dtag.contains("..")
+        && dtag
+            .chars()
+            .all(|c| c.is_ascii_alphanumeric() || c == '.' || c == '_' || c == '-')
+}
+
 /// Build a `buzz://repo` link for a repository announcement (kind 30617).
 pub fn repo_link(owner: &str, repo_id: &str) -> String {
     format!("buzz://repo?owner={owner}&d={repo_id}")
 }
 
+/// Build a `buzz://project` link for a project announcement (kind 30621).
+pub fn project_link(owner: &str, project_id: &str) -> String {
+    format!("buzz://project?owner={owner}&d={project_id}")
+}
+
 /// Build a `buzz://pr` link for a pull request event (kind 1618).
 pub fn pull_request_link(event_id: &str, owner: &str, repo_id: &str) -> String {
     format!("buzz://pr?id={event_id}&owner={owner}&d={repo_id}")
@@ -47,5 +70,26 @@ mod tests {
             repo_link(OWNER, "buzz-world"),
             format!("buzz://repo?owner={OWNER}&d=buzz-world")
         );
+        assert_eq!(
+            project_link(OWNER, "buzz-world"),
+            format!("buzz://project?owner={OWNER}&d=buzz-world")
+        );
+    }
+
+    #[test]
+    fn linkable_dtag_matches_the_desktop_charset() {
+        for ok in ["buzz-world", "a", "a.b_c-d", &"a".repeat(64)] {
+            assert!(is_linkable_dtag(ok), "{ok:?} should be linkable");
+        }
+        for bad in [
+            "",
+            ".hidden",
+            "a..b",
+            "has space",
+            "sl/ash",
+            &"a".repeat(65),
+        ] {
+            assert!(!is_linkable_dtag(bad), "{bad:?} should not be linkable");
+        }
     }
 }