feat: add architecture guidance and capability-aware escalation to skills

Brainstorming: design-for-isolation guidance and brownfield codebase awareness
Writing-plans: file structure section requiring decomposition before task definition
Implementer prompt: code organization awareness, structured escalation protocol
  (DONE/DONE_WITH_CONCERNS/BLOCKED/NEEDS_CONTEXT), explicit permission to stop
Subagent-driven-development: provider-agnostic model selection tiers, escalation handling

skills/brainstorming/SKILL.md

@@ -73,6 +73,17 @@ digraph brainstorming {
 - Cover: architecture, components, data flow, error handling, testing
 - Be ready to go back and clarify if something doesn't make sense
 
+**Design for isolation and clarity:**
+- Break the system into smaller units that each have one clear purpose, communicate through well-defined interfaces, and can be understood and tested independently
+- For each unit, you should be able to answer: what does it do, how do you use it, and what does it depend on?
+- Can someone understand what a unit does without reading its internals? Can you change the internals without breaking consumers? If not, the boundaries need work.
+- Smaller, well-bounded units are also easier for you to work with - you reason better about code you can hold in context at once, and your edits are more reliable when files are focused. When a file grows large, that's often a signal that it's doing too much.
+
+**Working in existing codebases:**
+- Explore the current structure before proposing changes. Follow existing patterns.
+- Where existing code has problems that affect the work (e.g., a file that's grown too large, unclear boundaries, tangled responsibilities), include targeted improvements as part of the design - the way a good developer improves code they're working in.
+- Don't propose unrelated refactoring. Stay focused on what serves the current goal.
+
 ## After the Design
 
 **Documentation:**

skills/subagent-driven-development/SKILL.md

@@ -82,6 +82,33 @@ digraph process {
 }
 ```
 
+## Model Selection
+
+Use the least powerful model that can handle each role to conserve cost and increase speed.
+
+**Mechanical implementation tasks** (isolated functions, clear specs, 1-2 files): use a fast, cheap model. Most implementation tasks are mechanical when the plan is well-specified.
+
+**Integration and judgment tasks** (multi-file coordination, pattern matching, debugging): use a standard model.
+
+**Architecture, design, and review tasks**: use the most capable available model.
+
+**Task complexity signals:**
+- Touches 1-2 files with a complete spec → cheap model
+- Touches multiple files with integration concerns → standard model
+- Requires design judgment or broad codebase understanding → most capable model
+
+## Handling Escalation
+
+Implementer subagents may return with status BLOCKED or NEEDS_CONTEXT instead of DONE. This is expected and good - it means the implementer recognized the task was beyond its capability rather than producing bad work.
+
+**When an implementer escalates:**
+1. Assess whether more context would help - provide it and re-dispatch with the same model
+2. Re-dispatch with a more capable model if the task requires more reasoning
+3. Break the task into smaller, more tractable pieces
+4. Escalate to the human if the plan needs rethinking
+
+**Never** ignore an escalation or force the same model to retry without changes. If the implementer said it's stuck, something needs to change.
+
 ## Prompt Templates
 
 - `./implementer-prompt.md` - Dispatch implementer subagent

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

@@ -41,6 +41,36 @@ Task tool (general-purpose):
     **While you work:** If you encounter something unexpected or unclear, **ask questions**.
     It's always OK to pause and clarify. Don't guess or make assumptions.
 
+    ## Code Organization
+
+    You reason best about code you can hold in context at once, and your edits are more
+    reliable when files are focused. Keep this in mind:
+    - Follow the file structure defined in the plan
+    - Each file should have one clear responsibility with a well-defined interface
+    - If a file you're creating is growing beyond the plan's intent, consider whether
+      it should be split into smaller units with clear boundaries
+    - If an existing file you're modifying is already large or tangled, work carefully
+      and note it as a concern in your report
+    - In existing codebases, follow established patterns. Improve code you're touching
+      the way a good developer would, but don't restructure things outside your task.
+
+    ## When You're in Over Your Head
+
+    It is always OK to stop and say "this is too hard for me." Bad work is worse than
+    no work. You will not be penalized for escalating.
+
+    **STOP and escalate when:**
+    - The task requires architectural decisions with multiple valid approaches
+    - You need to understand code beyond what was provided and can't find clarity
+    - You feel uncertain about whether your approach is correct
+    - The task involves restructuring existing code in ways the plan didn't anticipate
+    - You've been reading file after file trying to understand the system without progress
+
+    **How to escalate:** Report back with status BLOCKED or NEEDS_CONTEXT. Describe
+    specifically what you're stuck on, what you've tried, and what kind of help you need.
+    The controller can provide more context, re-dispatch with a more capable model,
+    or break the task into smaller pieces.
+
     ## Before Reporting Back: Self-Review
 
     Review your work with fresh eyes. Ask yourself:
@@ -70,9 +100,14 @@ Task tool (general-purpose):
     ## Report Format
 
     When done, report:
-    - What you implemented
+    - **Status:** DONE | DONE_WITH_CONCERNS | BLOCKED | NEEDS_CONTEXT
+    - What you implemented (or what you attempted, if blocked)
     - What you tested and test results
     - Files changed
     - Self-review findings (if any)
     - Any issues or concerns
+
+    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.
 ```

skills/writing-plans/SKILL.md

@@ -18,6 +18,17 @@ Assume they are a skilled developer, but know almost nothing about our toolset o
 **Save plans to:** `docs/superpowers/plans/YYYY-MM-DD-<feature-name>.md`
 - (User preferences for plan location override this default)
 
+## File Structure
+
+Before defining tasks, map out which files will be created or modified and what each one is responsible for. This is where decomposition decisions get locked in.
+
+- Design units with clear boundaries and well-defined interfaces. Each file should have one clear responsibility.
+- You work best with files you can read in a single pass. Large files cause silent truncation, context degradation, and unreliable edits. Prefer smaller, focused files over large ones that do too much.
+- Files that change together should live together. Split by responsibility, not by technical layer.
+- In existing codebases, follow established patterns. If the codebase uses large files, don't unilaterally restructure - but if a file you're modifying has grown unwieldy, including a split in the plan is reasonable.
+
+This structure informs the task decomposition. Each task should produce self-contained changes that make sense independently.
+
 ## Bite-Sized Task Granularity
 
 **Each step is one action (2-5 minutes):**