feat(infospace): add metrics history and viability tracking (S2.5)

History module with snapshot creation from check results, metrics file
I/O, auto-append to history after checks, date-based snapshot lookup,
and metric trend extraction. CLI commands: history, history-diff.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

markitect/infospace/cli.py

@@ -331,3 +331,91 @@ def check(config_path: Optional[str], concerns: tuple, as_json: bool):
         click.echo("Metrics summary:")
         for k, v in sorted(m.items()):
             click.echo(f"  {k}: {v:.4f}")
+
+    # Record to history
+    if m:
+        from markitect.infospace.history import record_check_results
+        snap = record_check_results(report, cfg, root, entity_count=len(entity_list))
+        if not as_json:
+            click.echo(f"\nRecorded snapshot {snap.snapshot_id}")
+
+
+# ── history ─────────────────────────────────────────────────────────
+
+
+@infospace_commands.command()
+@click.option("--config", "config_path", default=None, help="Path to infospace.yaml.")
+@click.option("--metric", default=None, help="Show trend for a specific metric.")
+@click.option("--json", "as_json", is_flag=True, help="Output as JSON.")
+def history(config_path: Optional[str], metric: Optional[str], as_json: bool):
+    """Show metrics history — snapshots over time."""
+    cfg, cfg_path = _load_config_or_exit(config_path)
+    root = cfg_path.parent
+
+    from markitect.infospace.history import get_history, metric_trend
+
+    snapshots = get_history(cfg, root)
+    if not snapshots:
+        click.echo("No history found. Run 'markitect infospace check' first.")
+        return
+
+    if metric:
+        trend = metric_trend(snapshots, metric)
+        if not trend:
+            click.echo(f"No data for metric '{metric}'.")
+            return
+        if as_json:
+            import json
+            click.echo(json.dumps(trend, indent=2))
+        else:
+            click.echo(f"Trend: {metric}\n")
+            for entry in trend:
+                click.echo(f"  {entry['date'][:19]}  {entry['value']:.4f}")
+        return
+
+    if as_json:
+        import json
+        click.echo(json.dumps([s.to_dict() for s in snapshots], indent=2, default=str))
+        return
+
+    click.echo(f"History: {len(snapshots)} snapshot(s)\n")
+    click.echo(f"{'#':<4} {'Date':<20} {'Entities':>8} {'Metrics':>8}")
+    click.echo("-" * 42)
+    for i, snap in enumerate(snapshots, 1):
+        date_str = snap.created_at.isoformat()[:19]
+        n_metrics = len(snap.collection_metrics)
+        click.echo(f"{i:<4} {date_str:<20} {snap.entity_count:>8} {n_metrics:>8}")
+
+
+@infospace_commands.command(name="history-diff")
+@click.argument("date_a")
+@click.argument("date_b")
+@click.option("--config", "config_path", default=None, help="Path to infospace.yaml.")
+def history_diff(date_a: str, date_b: str, config_path: Optional[str]):
+    """Compare two history snapshots by date (YYYY-MM-DD)."""
+    cfg, cfg_path = _load_config_or_exit(config_path)
+    root = cfg_path.parent
+
+    from markitect.infospace.history import find_snapshot_by_date, get_history
+    from markitect.infospace.evaluation_io import diff_snapshots
+
+    snapshots = get_history(cfg, root)
+    if len(snapshots) < 2:
+        click.echo("Need at least two snapshots to diff.")
+        return
+
+    snap_a = find_snapshot_by_date(snapshots, date_a)
+    snap_b = find_snapshot_by_date(snapshots, date_b)
+
+    if snap_a is None:
+        click.echo(f"No snapshot found near '{date_a}'.")
+        return
+    if snap_b is None:
+        click.echo(f"No snapshot found near '{date_b}'.")
+        return
+    if snap_a.snapshot_id == snap_b.snapshot_id:
+        click.echo("Both dates resolve to the same snapshot.")
+        return
+
+    diff = diff_snapshots(snap_a, snap_b)
+    click.echo(diff.summary())