docs: update session export panels and plan executor subplan wiring

- docs/reference/session_cli.md: add Rich output panels documentation
  for agents session export (Session Export, Contents, Integrity panels
  with example output); update success message to 'Export completed';
  add stdout export note and example (#3424)
- docs/reference/plan_execute.md: add Subplan Spawning section
  documenting SubplanService and SubplanExecutionService injection into
  PlanExecutor, execution flow (_spawn_subplans, _execute_subplans,
  _apply_subplan_results_to_plan), failure handling, and updated
  architecture diagram (#3561)

docs/reference/plan_execute.md

@@ -15,14 +15,78 @@ changeset capture through `ChangeSetStore`.
 
 ```
 PlanExecutor
-├── StrategizeStubActor     (read-only, produces decision tree)
-├── ExecuteStubActor         (legacy stub: sandbox + ChangeSetCapture)
-├── RuntimeExecuteActor      (runtime: ToolRunner + ChangeSetStore)
-├── PlanExecutionContext      (plan metadata + resource bindings)
-├── PlanLifecycleService      (phase transitions, persistence)
-└── ErrorRecoveryService      (optional — error recording + retry logic)
+├── StrategizeStubActor      (read-only, produces decision tree)
+├── ExecuteStubActor          (legacy stub: sandbox + ChangeSetCapture)
+├── RuntimeExecuteActor       (runtime: ToolRunner + ChangeSetStore)
+├── PlanExecutionContext       (plan metadata + resource bindings)
+├── PlanLifecycleService       (phase transitions, persistence)
+├── SubplanService             (optional — spawn child plans from decisions)
+├── SubplanExecutionService    (optional — execute spawned child plans)
+└── ErrorRecoveryService       (optional — error recording + retry logic)
 ```
 
+## Subplan Spawning (v3.8.0+)
+
+When a plan's Strategize phase records `subplan_spawn` or
+`subplan_parallel_spawn` decisions, the Execute phase automatically
+spawns and executes child plans via the injected `SubplanService` and
+`SubplanExecutionService`.
+
+### Wiring
+
+Both services are injected as optional constructor parameters:
+
+```python
+from cleveragents.application.services.plan_executor import PlanExecutor
+from cleveragents.application.services.subplan_service import SubplanService
+from cleveragents.application.services.subplan_execution_service import (
+    SubplanExecutionService,
+)
+
+executor = PlanExecutor(
+    lifecycle_service=lifecycle,
+    tool_runner=runner,
+    execution_context=ctx,
+    subplan_service=subplan_svc,          # optional
+    subplan_execution_service=exec_svc,   # optional
+)
+```
+
+When either service is `None`, all subplan spawning logic is skipped
+(backward-compatible no-op).
+
+### Execution Flow
+
+After the actor completes the Execute phase:
+
+1. **`_spawn_subplans()`** — queries `SubplanService.get_spawn_decisions()`
+   for the plan, then calls `SubplanService.spawn()` for each decision,
+   creating child plan records.
+2. **`_execute_subplans()`** — calls `SubplanExecutionService.execute_all()`,
+   routing sequential `subplan_spawn` decisions through ordered execution
+   and `subplan_parallel_spawn` groups through concurrent execution.
+3. **`_apply_subplan_results_to_plan()`** — propagates child plan failure
+   information back to the parent plan. When one or more child plans fail,
+   the parent plan's `error_details` field is annotated with a
+   `failed_subplan_ids` list.
+
+### Properties
+
+| Property | Type | Description |
+|----------|------|-------------|
+| `subplan_service` | `SubplanService \| None` | Injected subplan service |
+| `subplan_execution_service` | `SubplanExecutionService \| None` | Injected execution service |
+
+### Failure Handling
+
+Child plan failures are **annotated, not raised**. The parent plan
+continues to the Apply phase even if child plans fail; the
+`failed_subplan_ids` list in `error_details` allows downstream
+consumers to detect and handle failures.
+
+See [`subplan_service.md`](subplan_service.md) and
+[`subplans.md`](subplans.md) for full subplan API reference.
+
 ## Execution Modes
 
 | Mode    | Actor               | Trigger                           | Output                 |

docs/reference/session_cli.md

@@ -189,6 +189,45 @@ agents session export <SESSION_ID> [--output <FILE>] [--force] [--format <FORMAT
 | `--force` | | Overwrite existing output file |
 | `--format` | | Export format: `json` (default, re-importable) or `md` (Markdown transcript, lossy) |
 
+### Rich Output Panels
+
+On success, the `rich` format renders three panels:
+
+- **Session Export** — session ID, output path (or `(stdout)` for stdout), message count,
+  file size, and format.
+- **Contents** — messages count, plan references, metadata keys, actor config inclusion,
+  and schema version.
+- **Integrity** — SHA-256 checksum (`sha256:xxxx...xxxx`) and encrypted flag.
+
+Followed by a `✓ OK Export completed` success message.
+
+Example output:
+
+```
+╭─ Session Export ────────────────────╮
+│ Session: 01HXM2A6K1P2E9Q9D4GQ7J4S7Z │
+│ Output: /tmp/weekly-planning.json   │
+│ Messages: 6                         │
+│ Size: 24 KB                         │
+│ Format: JSON                        │
+╰─────────────────────────────────────╯
+
+╭─ Contents ─────────────────╮
+│ Messages: 6                │
+│ Plan References: 1         │
+│ Metadata Keys: 2           │
+│ Actor Config: included     │
+│ Schema Version: v3         │
+╰────────────────────────────╯
+
+╭─ Integrity ──────────────────╮
+│ Checksum: sha256:7a9b...42c1 │
+│ Encrypted: no                │
+╰──────────────────────────────╯
+
+✓ OK Export completed
+```
+
 ### Notes
 
 - Parent directories are created automatically when writing to a file.
@@ -197,6 +236,7 @@ agents session export <SESSION_ID> [--output <FILE>] [--force] [--format <FORMAT
 - The `md` format produces a human-readable Markdown transcript with session metadata,
   full message history (role/timestamp/content), and linked plan references. It cannot
   be re-imported.
+- When exporting to stdout, the output path in the panel shows `(stdout)`.
 
 ### Examples
 
@@ -209,6 +249,9 @@ agents session export 01HXYZ... --format md -o session.md
 
 # Overwrite existing file
 agents session export 01HXYZ... -o session.json --force
+
+# Export to stdout
+agents session export 01HXYZ...
 ```
 
 ---