Add top contributor heatmap (last 12 months, PRs)

New plot showing top 10 PR contributors broken down by month over a
trailing 12-month window. Rendered as a YlOrRd heatmap with cell
annotations — horizontal streaks reveal who's consistently active vs.
ramping. Rows are sorted by latest-month PR count (window total as
tiebreaker) to surface current momentum rather than historical totals.
Bot accounts (*[bot]) are excluded.

Adds a contributor_monthly CSV export in generate-summaries and the
matching plot_contributor_heatmap function in plot.py.

Verified against the GitHub search API: spot-checked 6 cells across
high-volume and low-volume contributors — all match exactly.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: pront

scripts/util/plot.py

@@ -167,6 +167,11 @@ def main():
                 exclude_labels=args.exclude_labels
             )
 
+        contributor_csv = os.path.join(args.input_dir, f"{prefix}.contributor_monthly.csv")
+        if os.path.exists(contributor_csv):
+            output_path = os.path.join(OUTPUT_DIR, f"{prefix}.contributors_top10_12m.png")
+            plot_contributor_heatmap(contributor_csv, table, output_path)
+
     # Discussion trends
     disc_prefix = f"{env['REPO_OWNER']}_{env['REPO_NAME']}_discussions"
     disc_csv = os.path.join(args.input_dir, f"{disc_prefix}.monthly_summary.csv")
@@ -467,5 +472,68 @@ def plot_label_state_counts(path, table, output_path, top_n, exclude_labels=None
         logging.warning(f"[{table}] Could not generate label count chart: {e}")
 
 
+def plot_contributor_heatmap(path, table, output_path, top_n=10, window_months=12):
+    try:
+        df = pd.read_csv(path)
+        if df.empty:
+            logging.warning(f"[{table}] Contributor CSV is empty: {path}")
+            return
+
+        df = df[~df["user_login"].str.endswith("[bot]", na=False)]
+        if df.empty:
+            logging.warning(f"[{table}] No non-bot contributors in {path}")
+            return
+
+        months_all = sorted(df["month"].dropna().unique())
+        window = months_all[-window_months:]
+        df = df[df["month"].isin(window)]
+        if df.empty:
+            logging.warning(f"[{table}] No contributor data in last {window_months} months")
+            return
+
+        totals = df.groupby("user_login")["count"].sum().sort_values(ascending=False)
+        top_users = totals.head(top_n).index.tolist()
+        df = df[df["user_login"].isin(top_users)]
+
+        pivot = (
+            df.pivot_table(index="user_login", columns="month", values="count", fill_value=0)
+              .reindex(index=top_users, columns=window, fill_value=0)
+        )
+
+        last_month = window[-1]
+        pivot = pivot.assign(_total=totals.reindex(pivot.index).values)
+        pivot = pivot.sort_values(by=[last_month, "_total"], ascending=False).drop(columns="_total")
+
+        fig, ax = plt.subplots(figsize=(12, 5))
+        im = ax.imshow(pivot.values, aspect="auto", cmap="YlOrRd")
+
+        ax.set_xticks(np.arange(len(window)))
+        ax.set_xticklabels(window, rotation=45, ha="right")
+        ax.set_yticks(np.arange(len(pivot.index)))
+        ax.set_yticklabels(pivot.index)
+
+        vmax = pivot.values.max() if pivot.values.size else 0
+        for i in range(pivot.shape[0]):
+            for j in range(pivot.shape[1]):
+                v = pivot.values[i, j]
+                if v > 0:
+                    color = "white" if v > vmax * 0.5 else "black"
+                    ax.text(j, i, int(v), ha="center", va="center", color=color, fontsize=9)
+
+        cbar = fig.colorbar(im, ax=ax)
+        cbar.set_label(f"{table} opened")
+
+        ax.set_title(f"Top {top_n} {table} contributors (last {window_months} months)", fontsize=16)
+        set_axis_labels(ax, "Month", "Contributor")
+        ax.grid(False)
+
+        plt.tight_layout()
+        plt.savefig(output_path)
+        logging.info(f"Saved plot to {output_path}")
+        plt.close()
+    except Exception as e:
+        logging.warning(f"[{table}] Could not generate contributor heatmap: {e}")
+
+
 if __name__ == "__main__":
     main()

src/commands/generate_summaries.rs

@@ -28,6 +28,8 @@ pub fn run(db: &str, config: &Config, exclude_labels: Option<&str>) -> Result<()
         export_overall_totals(&conn, out_dir, config, table, exc)?;
     }
 
+    export_contributor_monthly(&conn, out_dir, config, "pull_requests", exc)?;
+
     // Generate discussion summaries if the table exists
     let has_discussions: bool = conn
         .prepare("SELECT 1 FROM discussions LIMIT 1")
@@ -317,6 +319,31 @@ fn export_overall_totals(
     )
 }
 
+fn export_contributor_monthly(
+    conn: &Connection,
+    out_dir: &Path,
+    config: &Config,
+    table: &str,
+    exclude_labels: Option<&[String]>,
+) -> Result<()> {
+    let (wc, params) = build_where(table, exclude_labels, &["user_login IS NOT NULL"]);
+    let query = format!(
+        "SELECT substr({table}.created_at, 1, 7) AS month,
+                {table}.user_login AS user_login,
+                COUNT(*) AS count
+         FROM {table}
+         {wc}
+         GROUP BY month, user_login
+         ORDER BY month, count DESC"
+    );
+    write_query_to_csv(
+        conn,
+        &query,
+        &to_rusqlite_params(&params),
+        &csv_path(out_dir, config, table, "contributor_monthly"),
+    )
+}
+
 fn export_discussion_monthly_summary(
     conn: &Connection,
     out_dir: &Path,