fix(#785): type dump-manifests missing dir errors

Automation needs dump-manifests argument failures to classify without scraping prose, so the --manifests-dir missing-value paths now share the missing_flag_value contract and usage hint.

Constraint: Scope limited to ROADMAP #785 and existing rusty-claude-cli JSON error contracts.
Rejected: Broader dump-manifests parser cleanup | outside the requested ROADMAP #785 packaging scope.
Confidence: high
Scope-risk: narrow
Directive: Keep future dump-manifests argument errors typed and hint-bearing for JSON callers.
Tested: cargo test -p rusty-claude-cli --test output_format_contract -- dump_manifests_missing_dir_has_typed_kind_and_hint_785 --nocapture; cargo test -p rusty-claude-cli classify_error_kind_returns_correct_discriminants -- --nocapture; cargo fmt --all -- --check
Not-tested: full workspace test suite

ROADMAP.md

@@ -7735,3 +7735,6 @@ Original filing (2026-04-18): the session emitted `SessionStart hook (completed)
 783. **`claw --output-format json init` success envelope was missing `hint` field; idempotent re-init was not structurally detectable** — dogfooded 2026-05-27 on `32c9276f`. The init JSON envelope had no `hint` field (absent, not null), and no field to distinguish a fresh init from a re-init without checking `created.len() == 0`. Orchestrators had to inspect `created` array length to detect idempotent behavior. Fix: (1) added `hint` field to init JSON envelope — fresh path points at `CLAUDE.md + doctor`; idempotent path says "already initialised, run doctor"; (2) added `already_initialized: bool` field — `true` when `created` and `updated` are both empty (all artifacts skipped). Both test cases (fresh + re-init) covered by `init_json_envelope_has_hint_and_already_initialized_783`. 42 CLI contract tests pass. [SCOPE: claw-code] Source: Jobdori init-envelope probe on `32c9276f`, 2026-05-27.
 
 784. **`claw export` had two opaque arg-error paths returning `error_kind:"unknown"` + `hint:null`** — dogfooded 2026-05-27 on `81fe0ccb` (pinpoint by Gaebal-gajae). `claw export --output` (missing flag value) emitted plain `"missing value for --output"` with no typed prefix; `claw export a.md b.md` (extra positional) emitted plain `"unexpected export argument: second.md"`. Both classified as `unknown+null`. Fix: (1) `--output` missing-value error now uses `missing_flag_value:` prefix + `\n` usage hint; (2) extra positional now uses `unexpected_extra_args:` prefix + `\n` usage hint; (3) classifier `unexpected_extra_args` arm extended to match both `starts_with("unexpected extra arguments")` (prose form, #766) and `starts_with("unexpected_extra_args:")` (typed prefix form, #784). Integration test `export_arg_errors_have_typed_kind_and_hint_784` covers both paths. 43 CLI contract tests pass. [SCOPE: claw-code] Source: Gaebal-gajae pinpoint + Jobdori implementation on `81fe0ccb`, 2026-05-27.
+
+
+785. **`claw dump-manifests --manifests-dir` missing-value errors were untyped/no-hint** — dogfooded 2026-05-27 on `e628b4bb`. `claw dump-manifests --manifests-dir --output-format json` and `claw dump-manifests --manifests-dir= --output-format json` emitted plain `--manifests-dir requires a path`; both classified as `error_kind:"unknown"` with `hint:null`. Manifest dumping is an automation/bootstrap surface, so callers need a stable `missing_flag_value` instead of regexing prose. Fix: changed both missing path branches to `missing_flag_value:` + newline usage hint. Regression guard: `dump_manifests_missing_dir_has_typed_kind_and_hint_785`. [SCOPE: claw-code] Source: gaebal-gajae manifest-bootstrap dogfood probe on `e628b4bb`, 2026-05-27.

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

@@ -2156,14 +2156,14 @@ fn parse_dump_manifests_args(
         if arg == "--manifests-dir" {
             let value = args
                 .get(index + 1)
-                .ok_or_else(|| String::from("--manifests-dir requires a path"))?;
+                .ok_or_else(|| String::from("missing_flag_value: --manifests-dir requires a path.\nUsage: claw dump-manifests --manifests-dir <path>"))?;
             manifests_dir = Some(PathBuf::from(value));
             index += 2;
             continue;
         }
         if let Some(value) = arg.strip_prefix("--manifests-dir=") {
             if value.is_empty() {
-                return Err(String::from("--manifests-dir requires a path"));
+                return Err(String::from("missing_flag_value: --manifests-dir requires a path.\nUsage: claw dump-manifests --manifests-dir <path>"));
             }
             manifests_dir = Some(PathBuf::from(value));
             index += 1;

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

@@ -2216,6 +2216,58 @@ fn interactive_only_guard_batch_769_to_771() {
     }
 }
 
+#[test]
+fn dump_manifests_missing_dir_has_typed_kind_and_hint_785() {
+    // #785: dump-manifests had two stale single-line --manifests-dir errors.
+    // JSON callers got error_kind:"unknown" + hint:null instead of a typed
+    // missing_flag_value they can route without prose scraping.
+    let root = unique_temp_dir("dump-manifests-missing-dir-785");
+    fs::create_dir_all(&root).expect("temp dir should exist");
+
+    let cases: &[&[&str]] = &[
+        &[
+            "--output-format",
+            "json",
+            "dump-manifests",
+            "--manifests-dir",
+        ],
+        &[
+            "--output-format",
+            "json",
+            "dump-manifests",
+            "--manifests-dir=",
+        ],
+    ];
+
+    for args in cases {
+        let output = run_claw(&root, args, &[]);
+        assert!(
+            !output.status.success(),
+            "claw {} should exit non-zero",
+            args.join(" ")
+        );
+        let stderr = String::from_utf8_lossy(&output.stderr);
+        let json_line = stderr
+            .lines()
+            .find(|l| l.trim_start().starts_with('{'))
+            .unwrap_or_else(|| panic!("stderr should contain JSON for {:?}, got: {stderr}", args));
+        let parsed: serde_json::Value = serde_json::from_str(json_line)
+            .expect("dump-manifests arg error envelope should be valid JSON");
+        assert_eq!(
+            parsed["error_kind"], "missing_flag_value",
+            "claw {:?} must return missing_flag_value (#785): {parsed}",
+            args
+        );
+        assert!(
+            parsed["hint"]
+                .as_str()
+                .map_or(false, |h| h.contains("dump-manifests")),
+            "claw {:?} must expose dump-manifests usage hint (#785): {parsed}",
+            args
+        );
+    }
+}
+
 #[test]
 fn resume_plugin_mutations_are_typed_interactive_only_777() {
     // #777: `/plugins install|enable|disable|uninstall|update` in resume mode returned