Land eval-tuned combo: file handoffs, progress ledger, final-review package, REQUIRED model lines, reviewer risk budget

Validated 2026-06-10 (all gates pass): go-fractals 54.1-54.7 min / $12.81-14.31
(baseline 64.9 / $16.07); svelte-todo 55.0 min / 19.3M / $14.99 (baseline
79.7 / 27.3M / $20.98); planted-defect pass $2.77. Dispatch-model discipline
3/3 runs after moving model: into the templates as a REQUIRED line.
Full experiment log: evals docs/experiments/2026-06-10-sdd-cost-experiments.md

skills/subagent-driven-development/implementer-prompt.md

@@ -5,12 +5,15 @@ Use this template when dispatching an implementer subagent.
 ```
 Subagent (general-purpose):
   description: "Implement Task N: [task name]"
+  model: [MODEL — REQUIRED: choose per SKILL.md Model Selection; an omitted
+         model silently inherits the session's most expensive one]
   prompt: |
     You are implementing Task N: [task name]
 
     ## Task Description
 
-    [FULL TEXT of task from plan - paste it here, don't make subagent read file]
+    Read your task brief first: [BRIEF_FILE]
+    It contains the full task text from the plan.
 
     ## Context
 
@@ -104,13 +107,12 @@ Subagent (general-purpose):
     ## After Review Findings
 
     If a reviewer finds issues and you fix them, re-run the tests that cover
-    the amended code and include the results in your fix report. Reviewers
+    the amended code and append the results to your report file. Reviewers
     will not re-run tests for you — your report is the test evidence.
 
     ## Report Format
 
-    When done, report:
-    - **Status:** DONE | DONE_WITH_CONCERNS | BLOCKED | NEEDS_CONTEXT
+    Write your full report to [REPORT_FILE]:
     - What you implemented (or what you attempted, if blocked)
     - What you tested and test results
     - **TDD Evidence** (if TDD was required for this task):
@@ -120,6 +122,17 @@ Subagent (general-purpose):
     - Self-review findings (if any)
     - Any issues or concerns
 
+    Then report back with ONLY (under 15 lines — the detail lives in the
+    report file):
+    - **Status:** DONE | DONE_WITH_CONCERNS | BLOCKED | NEEDS_CONTEXT
+    - Commits created (short SHA + subject)
+    - One-line test summary (e.g. "14/14 passing, output pristine")
+    - Your concerns, if any
+    - The report file path
+
+    If BLOCKED or NEEDS_CONTEXT, put the specifics in the final message
+    itself — the controller acts on it directly.
+
     Use DONE_WITH_CONCERNS if you completed the work but have doubts about correctness.
     Use BLOCKED if you cannot complete the task. Use NEEDS_CONTEXT if you need
     information that wasn't provided. Never silently produce work you're unsure about.