docs: add architecture diagram

docs/architecture.md

@@ -0,0 +1,162 @@
+# Forge Architecture
+
+## System Overview
+
+```mermaid
+flowchart TD
+    subgraph External["External Systems"]
+        Jira
+        GitHub
+        Langfuse["Langfuse (Observability)"]
+    end
+
+    subgraph API["FastAPI Server (:8000)"]
+        JiraWH["POST /webhooks/jira"]
+        GitHubWH["POST /webhooks/github"]
+    end
+
+    subgraph Queue["Redis"]
+        Streams["Streams: forge:events:jira\nforge:events:github"]
+        State["AsyncRedisSaver\nLangGraph checkpointing"]
+    end
+
+    subgraph Router["WorkflowRouter"]
+        Route{"Route by\nissue type"}
+        Feature["FeatureWorkflow\n(Feature/Story)"]
+        Bug["BugWorkflow\n(Bug)"]
+        Task["TaskTakeoverWorkflow\n(Task/Epic)"]
+    end
+
+    subgraph Container["Podman Container (ephemeral)"]
+        Agent["Deep Agents + MCP\n/workspace (repo mounted)"]
+    end
+
+    LLM["LLM Backends\nAnthropic API (Claude)\nVertex AI (Claude/Gemini)"]
+
+    Jira -- webhooks --> JiraWH
+    GitHub -- webhooks --> GitHubWH
+    JiraWH --> Streams
+    GitHubWH --> Streams
+    Streams --> Route
+    Route --> Feature
+    Route --> Bug
+    Route --> Task
+    Feature --> Container
+    Bug --> Container
+    Task --> Container
+    Router <--> LLM
+    Container <--> LLM
+    Router --> Jira
+    Router --> GitHub
+    Router --> Langfuse
+```
+
+## Feature Ticket Lifecycle
+
+```mermaid
+flowchart TD
+    A["Jira ticket created\nforge:managed (Feature/Story)"] --> B[generate_prd]
+    B --> C[">> prd_approval_gate"]
+    C --> D[generate_spec]
+    D --> E[">> spec_approval_gate"]
+    E --> F[decompose_epics]
+    F --> G[">> plan_approval_gate"]
+    G --> H[generate_tasks]
+    H --> I[">> task_approval_gate"]
+    I --> J["task_router (per-repo)"]
+
+    J --> K[setup_workspace]
+    K --> L["implement_task\n(Podman + Deep Agents)"]
+    L --> M[local_review]
+    M -->|"needs work (up to 2x)"| L
+    M --> N[update_documentation]
+    N --> O[create_pr]
+    O --> P["teardown_workspace"]
+    P -->|more repos| K
+
+    P --> Q[wait_for_ci_gate]
+    Q --> R{ci_evaluator}
+    R -->|fail| S["attempt_ci_fix\n(up to 5x)"]
+    S --> Q
+    R -->|pass| T[">> human_review_gate"]
+    T -->|changes_requested| U[implement_review]
+    U --> Q
+    T -->|approved| V["complete_tasks\naggregate_epic_status\naggregate_feature_status\nEND"]
+```
+
+`>>` = human checkpoint (auto-approved when `forge:yolo` label is set)
+
+## Bug Ticket Lifecycle
+
+```mermaid
+flowchart TD
+    A["Jira ticket created\nforge:managed (Bug)"] --> B[triage_check]
+    B -->|missing fields| C[">> triage_gate"]
+    C --> B
+    B -->|sufficient| D[analyze_bug]
+    D --> E["reflect_rca\n(up to 3 cycles)"]
+    E --> D
+    D --> F[">> rca_option_gate\nuser selects >option N"]
+    F --> G[plan_bug_fix]
+    G --> H[">> plan_approval_gate"]
+    H --> I[decompose_plan]
+
+    I --> J[setup_workspace]
+    J --> K["implement_bug_fix\n(Podman + Deep Agents)"]
+    K --> L[local_review]
+    L -->|"needs work"| K
+    L --> M[update_documentation]
+    M --> N[create_pr]
+    N --> O[teardown_workspace]
+    O -->|more repos| J
+
+    O --> P[wait_for_ci_gate]
+    P --> Q{ci_evaluator}
+    Q -->|fail| R["attempt_ci_fix"]
+    R --> P
+    Q -->|pass| S[">> human_review_gate"]
+    S -->|changes_requested| T[implement_review]
+    T --> P
+    S -->|merged| U[post_merge_summary]
+    U --> V[END]
+```
+
+## Task Ticket Lifecycle
+
+```mermaid
+flowchart TD
+    A["Jira ticket created\nforge:managed (Task/Epic)"] --> B[triage_check]
+    B -->|missing context| C[">> triage_gate\nforge:task-triage-pending"]
+    C --> B
+    B -->|sufficient| D[generate_plan]
+    D --> E[">> task_plan_approval_gate\nforge:plan-pending"]
+    E -->|"? question"| F[answer_question]
+    F --> E
+    E -->|"! feedback"| D
+    E -->|approved| G[setup_workspace]
+
+    G --> H["execute_task_changes\n(Podman + Deep Agents)"]
+    H --> I[qualitative_review]
+    I -->|"needs work (up to 2x)"| H
+    I -->|adequate| J[create_pr]
+    J --> K[teardown_workspace]
+    K -->|more repos| G
+
+    K --> L[wait_for_ci_gate]
+    L --> M{ci_evaluator}
+    M -->|fail| N["attempt_ci_fix"]
+    N --> L
+    M -->|pass| O[">> human_review_gate"]
+    O -->|changes_requested| P[implement_review]
+    P --> L
+    O -->|merged| Q[complete_task_takeover]
+```
+
+## Data Flow Summary
+
+- **Inbound events:** Jira/GitHub webhooks --> FastAPI --> Redis Streams
+- **State persistence:** Redis (LangGraph AsyncRedisSaver, keyed by ticket)
+- **LLM calls:** Orchestrator nodes and container agents --> Claude/Gemini (Anthropic / Vertex AI), bidirectional
+- **Code execution:** implement_task --> Podman container --> Deep Agents (library)
+- **Outbound actions:** Jira (comments, labels, transitions), GitHub (PRs, branches, reviews)
+- **Observability:** Langfuse (LLM traces, workflow spans, costs)