fix(#787): --resume with directory path returns session_path_is_directory kind + hint; wire fallback_hint_for_error_kind into both resume error emission sites

rust/crates/rusty-claude-cli/src/main.rs

@@ -283,6 +283,9 @@ fn classify_error_kind(message: &str) -> &'static str {
         // error message is "failed to restore session: legacy session is missing workspace
         // binding: ...", so the specific arm must be checked first.
         "legacy_session_no_workspace_binding"
+    } else if message.contains("Is a directory") || message.contains("os error 21") {
+        // #787: --resume given a directory path instead of a .jsonl file
+        "session_path_is_directory"
     } else if message.contains("failed to restore session") {
         "session_load_failed"
     } else if message.contains("unsupported ACP invocation") {
@@ -401,6 +404,13 @@ fn fallback_hint_for_error_kind(kind: &str) -> Option<&'static str> {
         "missing_credentials" => {
             Some("Set ANTHROPIC_API_KEY or ANTHROPIC_AUTH_TOKEN before running claw.")
         }
+        // #787: session load failures have no \n-delimited hint from the OS error path
+        "session_load_failed" => Some(
+            "Pass a path to a .jsonl session file, not a directory. Managed sessions live in .claw/sessions/.",
+        ),
+        "session_path_is_directory" => Some(
+            "--resume expects a .jsonl session file path, not a directory. Run `claw --output-format json /session list` to list managed sessions.",
+        ),
         _ => None,
     }
 }
@@ -3327,7 +3337,10 @@ fn resume_session(session_path: &Path, commands: &[String], output_format: CliOu
                 // #77: classify session load errors for downstream consumers
                 let full_message = format!("failed to restore session: {error}");
                 let kind = classify_error_kind(&full_message);
-                let (short_reason, hint) = split_error_hint(&full_message);
+                let (short_reason, inline_hint) = split_error_hint(&full_message);
+                // #787: fall back to kind-derived hint when message has no \n delimiter
+                let hint =
+                    inline_hint.or_else(|| fallback_hint_for_error_kind(kind).map(String::from));
                 eprintln!(
                     "{}",
                     serde_json::json!({
@@ -3472,7 +3485,10 @@ fn resume_session(session_path: &Path, commands: &[String], output_format: CliOu
                     // hardcoded "resume_command_error" + prose in the error field
                     let full_error = error.to_string();
                     let error_kind = classify_error_kind(&full_error);
-                    let (short_reason, hint) = split_error_hint(&full_error);
+                    let (short_reason, inline_hint) = split_error_hint(&full_error);
+                    // #787: fall back to kind-derived hint when error has no \n delimiter
+                    let hint = inline_hint
+                        .or_else(|| fallback_hint_for_error_kind(error_kind).map(String::from));
                     eprintln!(
                         "{}",
                         serde_json::json!({
@@ -13009,6 +13025,11 @@ mod tests {
             classify_error_kind("failed to restore session: file not found"),
             "session_load_failed"
         );
+        // #787: directory-as-session-path gets its own kind (precedes generic session_load_failed)
+        assert_eq!(
+            classify_error_kind("failed to restore session: Is a directory (os error 21)"),
+            "session_path_is_directory"
+        );
         assert_eq!(
             classify_error_kind("unrecognized argument `--foo` for subcommand `doctor`"),
             "cli_parse"

rust/crates/rusty-claude-cli/tests/output_format_contract.rs

@@ -2612,3 +2612,55 @@ fn dump_manifests_missing_dir_has_typed_kind_and_hint_786() {
         .expect("missing_flag_value must have hint (#786)");
     assert!(!h2.is_empty(), "hint must not be empty");
 }
+
+#[test]
+fn resume_directory_path_returns_typed_kind_and_hint_787() {
+    // #787: `claw --resume /tmp` (directory instead of .jsonl file) returned
+    // error_kind:"session_load_failed" + hint:null. The OS error "Is a directory (os error 21)"
+    // had no \n delimiter so split_error_hint returned None, and the resume error path
+    // didn't call fallback_hint_for_error_kind.
+    // Fix: (1) added session_path_is_directory classifier arm for os error 21;
+    //      (2) wired fallback_hint_for_error_kind into both resume error emission sites.
+    let root = unique_temp_dir("resume-dir-787");
+    fs::create_dir_all(&root).expect("temp dir");
+    std::process::Command::new("git")
+        .args(["init", "-q"])
+        .current_dir(&root)
+        .output()
+        .ok();
+
+    // Pass the root directory itself as the session path
+    let output = run_claw(
+        &root,
+        &[
+            "--output-format",
+            "json",
+            "--resume",
+            root.to_str().unwrap(),
+            "/status",
+        ],
+        &[],
+    );
+    assert!(
+        !output.status.success(),
+        "resume with directory should fail"
+    );
+    let stderr = String::from_utf8_lossy(&output.stderr);
+    let j: serde_json::Value = stderr
+        .lines()
+        .find(|l| l.trim_start().starts_with('{'))
+        .and_then(|l| serde_json::from_str(l).ok())
+        .expect("resume with directory should emit JSON error");
+    assert_eq!(
+        j["error_kind"], "session_path_is_directory",
+        "directory resume path should return session_path_is_directory, got {:?}",
+        j["error_kind"]
+    );
+    let hint = j["hint"]
+        .as_str()
+        .expect("session_path_is_directory must have hint (#787)");
+    assert!(
+        hint.contains(".jsonl") || hint.contains("session") || hint.contains("file"),
+        "hint should explain expected path format, got: {hint:?}"
+    );
+}