diff --git a/ROADMAP.md b/ROADMAP.md
index c8085dfa..1ff7b1f1 100644
--- a/ROADMAP.md
+++ b/ROADMAP.md
@@ -7719,3 +7719,5 @@ Original filing (2026-04-18): the session emitted `SessionStart hook (completed)
 775. **Missing integration tests for #769-#771 interactive-only guards and #774 hint fields** — dogfooded 2026-05-27 on `c760a49c`. Fixes #769-#771 (session/cost/clear/memory/ultraplan/model/usage/stats/fork interactive-only guards) and #774 (agents/plugins/mcp unknown-subcommand hints) had no integration tests — a regression in any of those 10+ match arms would go undetected. Also: classify_error_kind unit test for `unknown_agents_subcommand` used the old single-line format string, not the `\n`-delimited format emitted after #774. Fixed: (1) updated unit test string to match new `\n`-delimited emission; (2) added `agents_plugins_mcp_unknown_subcommand_have_hint_774` asserting `error_kind` + non-null `hint` for all three; (3) added `interactive_only_guard_batch_769_to_771` asserting `interactive_only` + non-null `hint` for 10 cases. 38 CLI contract tests pass. [SCOPE: claw-code] Source: Jobdori test-coverage sweep on `c760a49c`, 2026-05-27.
 
 776. **Resume-mode JSON errors had opaque `error_kind:"resume_command_error"` + `hint:null`** — dogfooded 2026-05-27 on `028998d0` (pinpoint identified by Gaebal-gajae). `run_resume_command` returned errors (e.g. from `parse_history_count`) with hardcoded `error_kind:"resume_command_error"` and the full error string in `error` with no hint extraction. Wrappers had to regex prose instead of switching on typed fields. Three co-located gaps fixed: (1) `resume_session` JSON error path now applies `classify_error_kind` + `split_error_hint` so errors get specific `error_kind` (e.g. `invalid_history_count`) and non-null `hint`; (2) `parse_history_count` errors now use `invalid_history_count:` prefix + `\n` usage hint; (3) `/session exists|delete|switch|fork` missing-arg and unsupported-action errors now use `\n`-delimited format with `unsupported_resumed_command:` prefix. Existing test updated to match new error message format. 38 CLI contract tests pass. [SCOPE: claw-code] Source: Gaebal-gajae pinpoint + Jobdori implementation on `028998d0`, 2026-05-27.
+
+777. **Resumed `/plugins install|enable|disable|uninstall|update` returned opaque error_kind instead of interactive_only** — dogfooded 2026-05-27 on `2684737d` (pinpoint by Gaebal-gajae). The mutation arm in `run_resume_command` returned a bare single-line error; after #776 it was classified/split by the caller but fell to `error_kind:"unknown"` + `hint:null` because there was no `interactive_only:` prefix. Orchestrators had no stable signal to distinguish "command rejected — switch to REPL" from a transient error. Fix: each mutation verb now returns `interactive_only: /plugins {action} requires a live session...\n...hint...` so the caller emits `error_kind:"interactive_only"` + non-null hint pointing at REPL or direct CLI. Integration test `resume_plugin_mutations_are_typed_interactive_only_777` covers all 5 mutation verbs. 39 CLI contract tests pass. [SCOPE: claw-code] Source: Gaebal-gajae pinpoint + Jobdori implementation on `2684737d`, 2026-05-27.
diff --git a/rust/crates/rusty-claude-cli/src/main.rs b/rust/crates/rusty-claude-cli/src/main.rs
index 18dbf8bf..0a8e063f 100644
--- a/rust/crates/rusty-claude-cli/src/main.rs
+++ b/rust/crates/rusty-claude-cli/src/main.rs
@@ -4475,11 +4475,13 @@ fn run_resume_command(
         SlashCommand::Plugins { action, target } => {
             // Only list is supported in resume mode (no runtime to reload)
             match action.as_deref() {
-                Some("install") | Some("uninstall") | Some("enable") | Some("disable")
-                | Some("update") => {
-                    return Err(
-                        "resumed /plugins mutations are interactive-only; start `claw` and run `/plugins` in the REPL".into(),
-                    );
+                Some(action @ ("install" | "uninstall" | "enable" | "disable" | "update")) => {
+                    // #777: use interactive_only: prefix + \n hint so #776's classify/split
+                    // emits error_kind:interactive_only + non-null hint instead of unknown+null.
+                    // Orchestrators can now detect this and switch to a live REPL instead of retrying.
+                    return Err(format!(
+                        "interactive_only: /plugins {action} requires a live session to reload the plugin runtime.\nStart `claw` and run `/plugins {action}` inside the REPL, or use `claw plugins {action}` as a direct CLI command."
+                    ).into());
                 }
                 _ => {}
             }
diff --git a/rust/crates/rusty-claude-cli/tests/output_format_contract.rs b/rust/crates/rusty-claude-cli/tests/output_format_contract.rs
index dbf39c3b..02a0ec37 100644
--- a/rust/crates/rusty-claude-cli/tests/output_format_contract.rs
+++ b/rust/crates/rusty-claude-cli/tests/output_format_contract.rs
@@ -2215,3 +2215,63 @@ fn interactive_only_guard_batch_769_to_771() {
         );
     }
 }
+
+#[test]
+fn resume_plugin_mutations_are_typed_interactive_only_777() {
+    // #777: `/plugins install|enable|disable|uninstall|update` in resume mode returned
+    // a generic single-line error; after #776's classify/split it fell to
+    // error_kind:"unknown" + hint:null because there was no interactive_only: prefix.
+    // Fix: each mutation arm now returns "interactive_only: ... \n..." so the caller
+    // gets error_kind:interactive_only + non-null hint pointing at live REPL.
+    let root = unique_temp_dir("resume-plugin-mutations-777");
+    fs::create_dir_all(&root).expect("temp dir should exist");
+    std::process::Command::new("git")
+        .args(["init", "-q"])
+        .current_dir(&root)
+        .output()
+        .ok();
+
+    // Create a minimal session file so we get past session load and into command dispatch
+    let session_file = write_session_fixture(&root, "resume-plugin-777", None);
+
+    for mutation in &["install", "enable", "disable", "uninstall", "update"] {
+        let cmd = format!("/plugins {mutation} my-plugin");
+        let output = run_claw(
+            &root,
+            &[
+                "--resume",
+                session_file.to_str().unwrap(),
+                "--output-format",
+                "json",
+                &cmd,
+            ],
+            &[],
+        );
+        assert!(
+            !output.status.success(),
+            "/plugins {mutation} in resume mode should exit non-zero"
+        );
+        let stderr = String::from_utf8_lossy(&output.stderr);
+        let json_line = stderr
+            .lines()
+            .find(|l| l.trim_start().starts_with('{'))
+            .unwrap_or_else(|| {
+                panic!("/plugins {mutation} should emit JSON error, got stderr: {stderr}")
+            });
+        let parsed: serde_json::Value = serde_json::from_str(json_line).unwrap();
+        assert_eq!(
+            parsed["error_kind"], "interactive_only",
+            "/plugins {mutation} must return interactive_only, got {:?}",
+            parsed["error_kind"]
+        );
+        let hint = parsed["hint"].as_str().unwrap_or("");
+        assert!(
+            !hint.is_empty(),
+            "/plugins {mutation} must have non-null hint (#777)"
+        );
+        assert!(
+            hint.contains("claw") || hint.contains("REPL") || hint.contains("plugins"),
+            "/plugins {mutation} hint must reference live session or CLI, got: {hint:?}"
+        );
+    }
+}