feat: add parallel execution support for workflow steps (UI-only)

progi/alembic/versions/0006_parallel_edge.py

@@ -0,0 +1,28 @@
+"""add parallel column to step_edges
+
+Revision ID: 0006
+Revises: 0005
+Create Date: 2026-06-27
+"""
+
+from typing import Sequence, Union
+
+import sqlalchemy as sa
+from alembic import op
+
+revision: str = "0006"
+down_revision: Union[str, None] = "0005"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    with op.batch_alter_table("step_edges") as batch_op:
+        batch_op.add_column(
+            sa.Column("parallel", sa.Boolean(), nullable=False, server_default="0")
+        )
+
+
+def downgrade() -> None:
+    with op.batch_alter_table("step_edges") as batch_op:
+        batch_op.drop_column("parallel")

progi/db.py

@@ -326,6 +326,7 @@ def save_workflow(
                         to_step_id=to_id,
                         condition=edge.get("condition"),
                         priority=edge.get("priority", 0),
+                        parallel=bool(edge.get("parallel", False)),
                     )
                 )
         else:
@@ -1073,6 +1074,7 @@ def get_workflow_with_playbooks(cfg: Config, workflow_id: int) -> dict[str, Any]
                 "to_step_id": e["to_step_id"],
                 "condition": e["condition"],
                 "priority": e["priority"],
+                "parallel": bool(e["parallel"]),
             }
             for e in edge_rows
         ],
@@ -1099,6 +1101,7 @@ def export_workflow(cfg: Config, workflow_id: int) -> dict[str, Any]:
                 "to": step_by_id[e["to_step_id"]]["name"],
                 "condition": e["condition"],
                 "priority": e["priority"],
+                "parallel": e.get("parallel", False),
             }
             for e in wf["edges"]
         ],
@@ -1169,6 +1172,7 @@ def get_step_detail(cfg: Config, workflow_id: int, step_id: int) -> dict[str, An
             "id": e["from_step_id"],
             "name": step_names.get(e["from_step_id"], str(e["from_step_id"])),
             "condition": e["condition"],
+            "parallel": bool(e["parallel"]),
         }
         for e in edge_rows
         if e["to_step_id"] == step_id
@@ -1178,6 +1182,7 @@ def get_step_detail(cfg: Config, workflow_id: int, step_id: int) -> dict[str, An
             "id": e["to_step_id"],
             "name": step_names.get(e["to_step_id"], str(e["to_step_id"])),
             "condition": e["condition"],
+            "parallel": bool(e["parallel"]),
         }
         for e in edge_rows
         if e["from_step_id"] == step_id

progi/models.py

@@ -73,6 +73,8 @@
     sa.Column("condition", sa.JSON, nullable=True),
     # edges evaluated in ascending priority; first match wins
     sa.Column("priority", sa.Integer, nullable=False, server_default="0"),
+    # when True, this edge is part of a parallel fork (rendered side-by-side)
+    sa.Column("parallel", sa.Boolean, nullable=False, server_default="0"),
 )
 
 playbooks = sa.Table(

progi/prompts/workflow_skeleton.md

@@ -89,6 +89,25 @@ For a branching workflow, the edges express the routing logic:
 - **Loops** are expressed as back-edges: an edge from a later step back to an
   earlier step. Use a conditional edge (priority 0) for the exit path and a
   second edge (priority 1, condition or `null`) for the loop-back.
+- **Parallel steps** — if two or more steps can be done at the same time
+  (they don't depend on each other's output), mark those edges with
+  `"parallel": true`. All edges in a parallel group must share the same
+  `from` step and have `"condition": null`. A join step after the group
+  receives the output of whichever parallel branch finished last (sequential
+  execution is unchanged — this flag only affects visualization).
+
+  Example — Research, Design, and Legal Review can all happen after Kickoff:
+
+  ```json
+  {"from": "Kickoff",         "to": "Research",      "condition": null, "priority": 0, "parallel": true},
+  {"from": "Kickoff",         "to": "Design",         "condition": null, "priority": 0, "parallel": true},
+  {"from": "Kickoff",         "to": "Legal Review",   "condition": null, "priority": 0, "parallel": true},
+  {"from": "Research",        "to": "Write Draft",    "condition": null, "priority": 0},
+  {"from": "Design",          "to": "Write Draft",    "condition": null, "priority": 0},
+  {"from": "Legal Review",    "to": "Write Draft",    "condition": null, "priority": 0}
+  ```
+
+  Non-parallel edges default to `"parallel": false` and can be omitted.
 
 ## After the user approves the skeleton
 

progi/web/static/app.js

@@ -318,16 +318,38 @@ function workflowEditor() {
         def += `  ${nodeId}["${label}"]\n`;
       });
 
-      // Add edges
+      // Add edges, grouping parallel forks into Mermaid's `A --> B & C` syntax
       if (edges.length > 0) {
+        // Group edges by from_step_id to detect parallel forks
+        const byFrom = {};
         edges.forEach(e => {
+          (byFrom[e.from_step_id] = byFrom[e.from_step_id] || []).push(e);
+        });
+
+        // Track which edges were already emitted as part of a parallel group
+        const emitted = new Set();
+
+        edges.forEach(e => {
+          if (emitted.has(e.id ?? `${e.from_step_id}-${e.to_step_id}`)) return;
+
           const from = `step_${e.from_step_id}`;
-          const to   = `step_${e.to_step_id}`;
-          if (e.condition) {
+          const siblings = byFrom[e.from_step_id] || [];
+          const parallelSiblings = siblings.filter(s => s.parallel);
+
+          if (e.parallel && parallelSiblings.length > 1) {
+            // Emit all parallel edges from this source as one `A --> B & C & D` line
+            const targets = parallelSiblings.map(s => `step_${s.to_step_id}`).join(' & ');
+            def += `  ${from} --> ${targets}\n`;
+            parallelSiblings.forEach(s => {
+              emitted.add(s.id ?? `${s.from_step_id}-${s.to_step_id}`);
+            });
+          } else if (e.condition) {
             const label = _conditionLabel(e.condition);
-            def += `  ${from} -->|"${label}"| ${to}\n`;
+            def += `  ${from} -->|"${label}"| step_${e.to_step_id}\n`;
+            emitted.add(e.id ?? `${e.from_step_id}-${e.to_step_id}`);
           } else {
-            def += `  ${from} --> ${to}\n`;
+            def += `  ${from} --> step_${e.to_step_id}\n`;
+            emitted.add(e.id ?? `${e.from_step_id}-${e.to_step_id}`);
           }
         });
       } else {

progi/web/templates/partials/step_detail.html

@@ -30,19 +30,24 @@ <h2 id="step-detail-title" class="text-sm font-semibold text-primary" x-text="st
           <template x-for="s in prevSteps" :key="s.id">
             <div class="flex items-start gap-3 rounded-lg bg-surface-1 px-3 py-2">
               <span class="text-accent text-xs mt-0.5">←</span>
-              <div>
-                <a
-                  href="#"
-                  @click.prevent="navigateStep(s.id)"
-                  class="text-xs text-accent font-medium hover:underline cursor-pointer"
-                  x-text="s.name"
-                ></a>
+              <div class="flex-1">
+                <div class="flex items-center gap-2">
+                  <a
+                    href="#"
+                    @click.prevent="navigateStep(s.id)"
+                    class="text-xs text-accent font-medium hover:underline cursor-pointer"
+                    x-text="s.name"
+                  ></a>
+                  <template x-if="s.parallel">
+                    <span class="text-[10px] font-medium px-1.5 py-0.5 rounded bg-surface-3 text-faint tracking-wide uppercase">parallel</span>
+                  </template>
+                </div>
                 <template x-if="s.condition">
                   <p class="text-xs text-muted mt-0.5"
                     x-text="`when ${s.condition.field} ${s.condition.operator} ${JSON.stringify(s.condition.value)}`">
                   </p>
                 </template>
-                <template x-if="!s.condition">
+                <template x-if="!s.condition && !s.parallel">
                   <p class="text-xs text-ghost mt-0.5">unconditional</p>
                 </template>
               </div>
@@ -63,19 +68,24 @@ <h2 id="step-detail-title" class="text-sm font-semibold text-primary" x-text="st
           <template x-for="s in nextSteps" :key="s.id">
             <div class="flex items-start gap-3 rounded-lg bg-surface-1 px-3 py-2">
               <span class="text-accent text-xs mt-0.5">→</span>
-              <div>
-                <a
-                  href="#"
-                  @click.prevent="navigateStep(s.id)"
-                  class="text-xs text-accent font-medium hover:underline cursor-pointer"
-                  x-text="s.name"
-                ></a>
+              <div class="flex-1">
+                <div class="flex items-center gap-2">
+                  <a
+                    href="#"
+                    @click.prevent="navigateStep(s.id)"
+                    class="text-xs text-accent font-medium hover:underline cursor-pointer"
+                    x-text="s.name"
+                  ></a>
+                  <template x-if="s.parallel">
+                    <span class="text-[10px] font-medium px-1.5 py-0.5 rounded bg-surface-3 text-faint tracking-wide uppercase">parallel</span>
+                  </template>
+                </div>
                 <template x-if="s.condition">
                   <p class="text-xs text-muted mt-0.5"
                     x-text="`when ${s.condition.field} ${s.condition.operator} ${JSON.stringify(s.condition.value)}`">
                   </p>
                 </template>
-                <template x-if="!s.condition">
+                <template x-if="!s.condition && !s.parallel">
                   <p class="text-xs text-ghost mt-0.5">unconditional</p>
                 </template>
               </div>