fix(endsession): parse arguments with the arg-parser so a slug with -h is no help request, and only the operator starts it

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

commands/trekendsession.md

@@ -2,6 +2,7 @@
 name: trekendsession
 description: Mark the current session as complete and write session-state pointing at the next session. Helper for informal multi-session flows.
 argument-hint: "<next-brief-path> <next-label> | --help"
+disable-model-invocation: true
 ---
 
 # Voyage End-Session Local v1.0
@@ -29,8 +30,25 @@ See **Handover 7** in `docs/HANDOVER-CONTRACTS.md` for the 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 the arg parser. Run this via the Bash tool at runtime
+(NOT eager-exec):
+
+```bash
+setopt nonomatch 2>/dev/null || true
+node ${CLAUDE_PLUGIN_ROOT}/lib/parsers/arg-parser.mjs --command trekendsession -- $ARGUMENTS
+```
+
+It prints the parse result as JSON. On exit 1, print its `errors` and stop.
+
+Print the usage block below and exit cleanly 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 declares no alias).
+
+Then do NOT proceed to any further phase. In every other case — a slug or a
+label that holds `-h` or `help` too — go on to Phase 1.
 
 ```
 /trekendsession — Mark current session done; point at next session.
@@ -76,8 +94,9 @@ Decision tree:
 
 ## Phase 2 — Required args check (headless-safe)
 
-Read `$ARGUMENTS`. Both `<next-brief-path>` and `<next-label>` are required.
-If either is missing or empty:
+Read the parse result from Phase 0: `<next-brief-path>` is `positional[0]`
+and `<next-label>` is `positional[1]`. Both are required. If either is
+missing or empty:
 
 ```
 Error: missing required args.
@@ -176,6 +195,7 @@ before retrying — usually means a bad path or label argument.
 - **Atomic write only.** Tmp + rename — no partial state files on disk.
 - **Zero secrets.** Status, paths, labels — never API keys, never user content
   beyond filenames.
-- **NEVER auto-invoke this command.** It is operator-typed only at session-end.
+- **NEVER auto-invoke this command.** It is operator-typed only at session-end
+  (the frontmatter field keeps the model from starting it; the operator types it).
 - **Idempotent within a session.** Running twice with the same args
   overwrites cleanly (atomic rename); does not double-advance.