fix: reject @-selectors in parseOrgProjectArg with helpful redirect

Fixes CLI-MH: 'Project @latest not found' when running 'sentry issues @latest'.

The @latest and @most_frequent magic selectors are only valid for
parseIssueArg (issue view/explain/plan), not for parseOrgProjectArg
(list commands). Previously, @ was not in RESOURCE_ID_FORBIDDEN so
'@latest' passed validation and entered project-search mode, leading
to a confusing ResolutionError.

Add rejectAtSelector() guard in:
- parseOrgProjectArg() bare-slug branch
- parseSlashOrgProject() both project slug branches (/@latest, org/@latest)

Known selectors get a redirect: 'Use: sentry issue view @latest'
Unknown @-prefixed values get: 'starts with @, slugs use letters/numbers/hyphens'

Author: BYK

src/lib/arg-parsing.ts

@@ -418,6 +418,38 @@ function issueArgFromUrl(parsed: ParsedSentryUrl): ParsedIssueArg | null {
   };
 }
 
+/**
+ * Reject `@`-prefixed values in org/project positions.
+ *
+ * `@latest` and `@most_frequent` are issue selectors supported by
+ * `parseIssueArg()` (for `issue view`, `explain`, `plan`). They are not
+ * valid project slugs. This guard provides a helpful redirect instead of
+ * the confusing "Project '@latest' not found" resolution error.
+ *
+ * Unknown `@`-prefixed values are also rejected — `@` is never valid in
+ * Sentry slugs.
+ */
+function rejectAtSelector(value: string, label: string): void {
+  if (!value.startsWith("@")) {
+    return;
+  }
+
+  const selector = parseSelector(value);
+  if (selector) {
+    throw new ValidationError(
+      `'${value}' is an issue selector, not a ${label}.\n` +
+        `  Use: sentry issue view ${value}`,
+      label
+    );
+  }
+
+  throw new ValidationError(
+    `Invalid ${label}: '${value}' starts with '@'.\n` +
+      "  Slugs contain only letters, numbers, hyphens, and underscores.",
+    label
+  );
+}
+
 /**
  * Parse a slash-delimited `org/project` string into a {@link ParsedOrgProject}.
  * Applies {@link normalizeSlug} to both components and validates against
@@ -435,6 +467,7 @@ function parseSlashOrgProject(input: string): ParsedOrgProject {
         'Invalid format: "/" requires a project slug (e.g., "/cli")'
       );
     }
+    rejectAtSelector(rawProject, "project slug");
     validateResourceId(rawProject, "project slug");
     const np = normalizeSlug(rawProject);
     return {
@@ -457,6 +490,7 @@ function parseSlashOrgProject(input: string): ParsedOrgProject {
   }
 
   // "sentry/cli" → explicit org and project
+  rejectAtSelector(rawProject, "project slug");
   validateResourceId(rawProject, "project slug");
   const np = normalizeSlug(rawProject);
   const normalized = no.normalized || np.normalized;
@@ -508,6 +542,7 @@ export function parseOrgProjectArg(arg: string | undefined): ParsedOrgProject {
     parsed = parseSlashOrgProject(trimmed);
   } else {
     // No slash → search for project across all orgs
+    rejectAtSelector(trimmed, "project slug");
     validateResourceId(trimmed, "project slug");
     const np = normalizeSlug(trimmed);
     parsed = {

test/lib/arg-parsing.test.ts

@@ -251,6 +251,54 @@ describe("parseOrgProjectArg", () => {
       expect(stderrOutput).not.toContain("Normalized slug");
     });
   });
+
+  describe("@-selector rejection", () => {
+    test("@latest throws with redirect to issue view", () => {
+      expect(() => parseOrgProjectArg("@latest")).toThrow(
+        "is an issue selector, not a project slug"
+      );
+      expect(() => parseOrgProjectArg("@latest")).toThrow(
+        "sentry issue view @latest"
+      );
+    });
+
+    test("@most_frequent throws with redirect to issue view", () => {
+      expect(() => parseOrgProjectArg("@most_frequent")).toThrow(
+        "is an issue selector, not a project slug"
+      );
+      expect(() => parseOrgProjectArg("@most_frequent")).toThrow(
+        "sentry issue view @most_frequent"
+      );
+    });
+
+    test("case-insensitive selector variants are rejected", () => {
+      expect(() => parseOrgProjectArg("@Latest")).toThrow(
+        "is an issue selector"
+      );
+      expect(() => parseOrgProjectArg("@LATEST")).toThrow(
+        "is an issue selector"
+      );
+      expect(() => parseOrgProjectArg("@mostFrequent")).toThrow(
+        "is an issue selector"
+      );
+    });
+
+    test("unknown @-prefixed value throws as invalid slug", () => {
+      expect(() => parseOrgProjectArg("@unknown")).toThrow("starts with '@'");
+    });
+
+    test("/@latest (leading slash) throws with redirect", () => {
+      expect(() => parseOrgProjectArg("/@latest")).toThrow(
+        "is an issue selector"
+      );
+    });
+
+    test("sentry/@latest (org/selector) throws with redirect", () => {
+      expect(() => parseOrgProjectArg("sentry/@latest")).toThrow(
+        "is an issue selector"
+      );
+    });
+  });
 });
 
 describe("parseIssueArg", () => {