feat(agents): run deep-bug-investigator synthesis on opus, pin tracks to sonnet (#133)

Co-authored-by: Oliver Kriska <oliver@ideax.sk>

Author: BugsBunny338

README.md

@@ -786,7 +786,7 @@ requirements can break unrelated migrations.
 | **workflow-orchestrator**    | opus   | project | Full cycle coordination (plan, work, review) |
 | **planning-orchestrator**    | opus   | project | Parallel research agent coordination         |
 | **parallel-reviewer**        | opus   | --      | 4-agent parallel code review                 |
-| **deep-bug-investigator**    | sonnet | --      | 4-track parallel bug investigation           |
+| **deep-bug-investigator**    | opus   | --      | 4-track parallel bug investigation           |
 | **call-tracer**              | sonnet | --      | Parallel call tree tracing                   |
 | **security-analyzer**        | opus   | --      | OWASP vulnerability scanning                 |
 | **context-supervisor**       | haiku  | --      | Multi-agent output compression               |

plugins/elixir-phoenix/agents/deep-bug-investigator.md

@@ -4,7 +4,7 @@ description: Deep bug investigation using 4 parallel subagents (reproduction, ro
 tools: Read, Grep, Glob, Bash, Agent, Write
 disallowedTools: Edit, NotebookEdit
 permissionMode: bypassPermissions
-model: sonnet
+model: opus
 effort: medium
 omitClaudeMd: true
 maxTurns: 30
@@ -214,12 +214,18 @@ mix compile --warnings-as-errors 2>&1 | head -50
 ### Phase 2: Spawn All 4 Subagents in Parallel
 
 ```
-Agent(subagent_type: "general-purpose", prompt: "Reproduction track...", run_in_background: true)
-Agent(subagent_type: "general-purpose", prompt: "Root cause track...", run_in_background: true)
-Agent(subagent_type: "general-purpose", prompt: "Impact track...", run_in_background: true)
-Agent(subagent_type: "general-purpose", prompt: "Fix strategy track...", run_in_background: true)
+Agent(subagent_type: "general-purpose", model: "sonnet", prompt: "Reproduction track...", run_in_background: true)
+Agent(subagent_type: "general-purpose", model: "sonnet", prompt: "Root cause track...", run_in_background: true)
+Agent(subagent_type: "general-purpose", model: "sonnet", prompt: "Impact track...", run_in_background: true)
+Agent(subagent_type: "general-purpose", model: "sonnet", prompt: "Fix strategy track...", run_in_background: true)
 ```
 
+**Always pass `model: "sonnet"` to the track subagents.** They do
+evidence gathering; without the explicit pin they inherit this
+orchestrator's model (opus), which would raise the cost of the whole
+fan-out without improving the evidence. Opus is reserved for the
+synthesis this orchestrator performs across the four tracks.
+
 **Agent prompts must be FOCUSED.** Scope each prompt to the
 relevant files, stack traces, and error context. Do NOT give
 vague prompts like "investigate the codebase."