feat(background_agent): Implement SOUL.md + Issue binding registry (Issues A-B) (#505)

- Create templates/SOUL.md template for agent souls
- Update CLAUDE.md with SOUL.md mandatory rules
- Update AGENTS.md with SOUL.md reference
- Create src/background_agent/db/issue_bindings.zig
- Extend Session struct with soul_file field
- Create src/tri/agent_commands.zig with spawn/run/stop
- Update main.zig routing for agent subcommands
- Update .gitignore to track issue_bindings.json and souls/

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

Author: Dmitrii Vasilev

.gitignore

@@ -99,6 +99,10 @@ zig/
 # Context index (generated binary, 80MB+)
 deploy/trinity-nexus/.context_index
 
+# SOUL bindings (tracked for orchestration)
+!.trinity/issue_bindings.json
+!.trinity/souls/
+
 # Temporary scripts
 check_ssh.py
 
@@ -312,6 +316,9 @@ fpga/tools/weight_pack_wide
 # Docker files in root (use deploy/ subdirectory instead)
 Dockerfile*
 *.toml
+
+# Templates (tracked for agent orchestration)
+!templates/SOUL.md
 fly.toml
 
 # Temporary directories
@@ -353,6 +360,11 @@ tree-sitter-vibee/
 trinity-nexus/
 website/
 
+# SOUL bindings (tracked for orchestration)
+!.trinity/issue_bindings.json
+!.trinity/souls/
+!templates/SOUL.md
+
 # Junk archive (large, local only)
 archive/junk-*/
 fpga/openxc7-synth/synth_reports/hslm_full_top.json
@@ -366,6 +378,7 @@ apps/queen/*.png
 data/cells/
 src/tools/uart-echo-test
 data/cifar-10/
+# Trinity: ignored except issue_bindings.json and souls/
 .trinity/
 .trinity/queen/
 .trinity/scholar/
@@ -374,3 +387,7 @@ data/cifar-10/
 .trinity/scholar/state/
 fpga/build-deps/
 fpga-flash
+# SOUL bindings (tracked - see lines 103-105)
+!.trinity/issue_bindings.json
+!.trinity/souls/
+!templates/SOUL.md

.trinity/mu/heartbeat.json

@@ -1 +1 @@
-{"agent":"mu","wake":161,"timestamp":1775215030,"errors_scanned":0,"fixes_applied":0,"build_ok":false,"test_ok":false}
+{"agent":"mu","wake":171,"timestamp":1775219479,"errors_scanned":0,"fixes_applied":0,"build_ok":false,"test_ok":false}

AGENTS.md

@@ -2,6 +2,25 @@
 
 Trinity S³AI implements a multi-agent swarm architecture using pure Zig. Each agent has a specific role and communicates through GitHub issues, JSONL events, and the unified `tri` CLI.
 
+## SOUL.md — Mandatory Agent Soul
+
+**Every agent/container MUST have `SOUL.md` at its root.**
+
+**SOUL.md contains:**
+- Agent type (Ralph / Mu / Scholar / Copywright / Oracle / Swarm / Custom)
+- Bound GitHub issue number
+- Mission statement
+- Allowed commands
+- Stop conditions
+- Reporting format (Protocol v2)
+- References to CLAUDE.md and AGENTS.md
+
+**Template**: `templates/SOUL.md`
+
+**All agents must follow CLAUDE.md law.**
+
+---
+
 ## Table of Contents
 
 - [Agent Types](#agent-types)