fix(resume): redirect --resume to the descendant that actually holds the messages

When context compression fires mid-session, run_agent's _compress_context
ends the current session, creates a new child session linked by
parent_session_id, and resets the SQLite flush cursor. New messages land
in the child; the parent row ends up with message_count = 0. A user who
runs 'hermes --resume <original_id>' sees a blank chat even though the
transcript exists — just under a descendant id.

PR #12920 already fixed the exit banner to print the live descendant id
at session end, but that didn't help users who resume by a session id
captured BEFORE the banner update (scripts, sessions list, old terminal
scrollback) or who type the parent id manually.

Fix: add SessionDB.resolve_resume_session_id() which walks the
parent→child chain forward and returns the first descendant with at
least one message row. Wire it into all three resume entry points:

  - HermesCLI._preload_resumed_session() (early resume at run() time)
  - HermesCLI._init_agent() (the classical resume path)
  - /resume slash command

Semantics preserved when the chain has no descendants with messages,
when the requested session already has messages, or when the id is
unknown. A depth cap of 32 guards against malformed loops.

This does NOT concatenate the pre-compression parent transcript into
the child — the whole point of compression is to shrink that, so
replaying it would blow the cache budget we saved. We just jump to
the post-compression child. The summary already reflects what was
compressed away.

Tests: tests/hermes_state/test_resolve_resume_session_id.py covers
  - the exact 6-session shape from the issue
  - passthrough when session has messages / no descendants
  - passthrough for nonexistent / empty / None input
  - middle-of-chain redirects
  - fork resolution (prefers most-recent child)

Closes #15000

cli.py

@@ -3254,6 +3254,23 @@ class HermesCLI:
                 _cprint(f"\033[1;31mSession not found: {self.session_id}{_RST}")
                 _cprint(f"{_DIM}Use a session ID from a previous CLI run (hermes sessions list).{_RST}")
                 return False
+            # If the requested session is the (empty) head of a compression
+            # chain, walk to the descendant that actually holds the messages.
+            # See #15000 and SessionDB.resolve_resume_session_id.
+            try:
+                resolved_id = self._session_db.resolve_resume_session_id(self.session_id)
+            except Exception:
+                resolved_id = self.session_id
+            if resolved_id and resolved_id != self.session_id:
+                ChatConsole().print(
+                    f"[{_DIM}]Session {_escape(self.session_id)} was compressed into "
+                    f"{_escape(resolved_id)}; resuming the descendant with your "
+                    f"transcript.[/]"
+                )
+                self.session_id = resolved_id
+                resolved_meta = self._session_db.get_session(self.session_id)
+                if resolved_meta:
+                    session_meta = resolved_meta
             restored = self._session_db.get_messages_as_conversation(self.session_id)
             if restored:
                 restored = [m for m in restored if m.get("role") != "session_meta"]
@@ -3472,6 +3489,22 @@ class HermesCLI:
             )
             return False
 
+        # If the requested session is the (empty) head of a compression chain,
+        # walk to the descendant that actually holds the messages. See #15000.
+        try:
+            resolved_id = self._session_db.resolve_resume_session_id(self.session_id)
+        except Exception:
+            resolved_id = self.session_id
+        if resolved_id and resolved_id != self.session_id:
+            self._console_print(
+                f"[dim]Session {self.session_id} was compressed into "
+                f"{resolved_id}; resuming the descendant with your transcript.[/]"
+            )
+            self.session_id = resolved_id
+            resolved_meta = self._session_db.get_session(self.session_id)
+            if resolved_meta:
+                session_meta = resolved_meta
+
         restored = self._session_db.get_messages_as_conversation(self.session_id)
         if restored:
             restored = [m for m in restored if m.get("role") != "session_meta"]
@@ -4686,6 +4719,22 @@ class HermesCLI:
             _cprint("  Use /history or `hermes sessions list` to see available sessions.")
             return
 
+        # If the target is the empty head of a compression chain, redirect to
+        # the descendant that actually holds the transcript. See #15000.
+        try:
+            resolved_id = self._session_db.resolve_resume_session_id(target_id)
+        except Exception:
+            resolved_id = target_id
+        if resolved_id and resolved_id != target_id:
+            _cprint(
+                f"  Session {target_id} was compressed into {resolved_id}; "
+                f"resuming the descendant with your transcript."
+            )
+            target_id = resolved_id
+            resolved_meta = self._session_db.get_session(target_id)
+            if resolved_meta:
+                session_meta = resolved_meta
+
         if target_id == self.session_id:
             _cprint("  Already on that session.")
             return