fix(ultraplan-local): Bug 1 — strict --help match + .md-arg diagnostic + Date.parse sort

Step 3 of v3.4.1 hot-fix plan. Three fixes in
commands/ultracontinue-local.md:

  - Phase 0: replace "$ARGUMENTS contains --help or -h" with parsed-arg
    dispatch via parseArgs(...,'ultracontinue'). Usage block fires only
    when flags['--help'] === true OR positional[0] === '-h'. Empty,
    whitespace, and project-dir args fall through to Phase 1
    (auto-discovery), which is the operator-default invocation.
  - Phase 1.a: NEW — reject .md positional arg with SC-2 diagnostic
    ("expected <project-dir>" + "did you mean to paste"). Operators
    pasting a NEXT-SESSION-PROMPT.local.md path see a clear error
    instead of a confusing fallthrough.
  - Phase 1.b: auto-discovery node -e now emits {path, updated_at}
    JSON per candidate; Phase 1 sorts numerically via
    Date.parse(updated_at) DESC instead of lexicographic compare.
    Newest in_progress wins, including across year-boundary timestamps.

All 4 Step 2 regression tests now green; full suite 322 → 333 passing.

plugins/ultraplan-local/commands/ultracontinue-local.md

@@ -30,8 +30,17 @@ See **Handover 7** in `docs/HANDOVER-CONTRACTS.md` for the full schema.
 
 ## Phase 0 — `--help` handling
 
-If `$ARGUMENTS` contains `--help` or `-h`, print the usage block below and exit
-cleanly. Do NOT proceed to any further phase.
+Parse `$ARGUMENTS` with `parseArgs($ARGUMENTS, 'ultracontinue')` from
+`lib/parsers/arg-parser.mjs`. Dispatch the usage block ONLY when one of these
+two conditions equals exactly true (no substring search, no "contains" check):
+
+- `flags['--help'] === true`, OR
+- `positional[0] === '-h'` (single-dash short form — the parser keeps it as
+  positional because the schema does not declare an alias).
+
+In every other case — including when `$ARGUMENTS` is empty, whitespace-only,
+the literal empty string `""`, or a positional project-dir — fall through to
+Phase 1. Do NOT print the usage block on empty args.
 
 ```
 /ultracontinue — Resume the next session in a multi-session ultraplan project.
@@ -65,32 +74,48 @@ Typical flow:
 
 ## Phase 1 — Resolve project directory
 
-If `$ARGUMENTS` is non-empty and not `--help`/`-h`, treat the first positional
-argument as the explicit `<project-dir>`. Otherwise auto-discover via Bash by
-enumerating `.claude/projects/*/.session-state.local.json` paths with `node -e`
-(NOT shell glob — harness-mode safety):
+The parsed `positional[0]` from Phase 0 is the explicit project-dir argument,
+when present. Otherwise (empty `$ARGUMENTS` or whitespace-only) auto-discover.
 
-```bash
-!`node -e "const fs=require('fs'),path=require('path');const root='.claude/projects';if(!fs.existsSync(root))process.exit(0);const dirs=fs.readdirSync(root).map(d=>path.join(root,d,'.session-state.local.json')).filter(p=>fs.existsSync(p));dirs.forEach(p=>process.stdout.write(p+'\\n'));"`
+### Step 1.a — Reject `.md` positional argument (SC-2)
+
+If `positional[0]` is non-empty AND ends in `.md`, the user almost certainly
+pasted a `NEXT-SESSION-PROMPT.local.md` path instead of a project directory.
+Print the following diagnostic to stderr and exit non-zero. Do NOT proceed.
+
+```
+Error: expected <project-dir>, got a markdown file path: <positional[0]>
+Did you mean to paste the file path as a project directory?
+Usage: /ultracontinue-local <project-dir>
 ```
 
-Decision tree:
+### Step 1.b — Auto-discover candidates
+
+When no explicit project-dir was given, enumerate
+`.claude/projects/*/.session-state.local.json` paths with `node -e`
+(NOT shell glob — harness-mode safety) and emit each as one JSON line of
+`{"path": ..., "updated_at": ...}` so Phase 1 can sort numerically:
+
+```bash
+!`node -e "const fs=require('fs'),path=require('path');const root='.claude/projects';if(!fs.existsSync(root))process.exit(0);for(const d of fs.readdirSync(root)){const p=path.join(root,d,'.session-state.local.json');if(!fs.existsSync(p))continue;let u='';try{u=(JSON.parse(fs.readFileSync(p,'utf8'))||{}).updated_at||''}catch(_){};process.stdout.write(JSON.stringify({path:p,updated_at:u})+'\\n');}"`
+```
+
+Sort the emitted candidates by `Date.parse(updated_at)` descending (newest
+first) — numeric comparison, NOT lexicographic string compare. The newest
+resumable state wins.
+
+### Step 1.c — Decision tree
 
 - **0 candidates and no explicit arg:** print SC-2 cold-start message and exit:
   ```
   No active multi-session project here.
   Start with /ultrabrief-local or /ultraplan-local.
   ```
-- **1 candidate (or explicit arg):** continue to Phase 2 with that path.
-- **>1 candidates and no explicit arg:** print all paths sorted by `updated_at`
-  descending, instruct the user to disambiguate via explicit `<project-dir>`,
-  then exit:
-  ```
-  Multiple active multi-session projects found:
-    .claude/projects/<a>/.session-state.local.json   updated <ts>
-    .claude/projects/<b>/.session-state.local.json   updated <ts>
-  Re-run as: /ultracontinue <project-dir>
-  ```
+- **1 candidate (or explicit non-`.md` arg):** continue to Phase 2 with that path.
+- **>1 candidates and no explicit arg:** with the Date.parse sort applied, the
+  newest resumable state wins automatically and the command continues to Phase 2
+  with that path. (Operators who want a different candidate re-invoke as
+  `/ultracontinue <project-dir>`.)
 
 ## Phase 2 — Validate the state file