feat(gemini): optimize context caching and TPM usage

[psklarkins]

Summary

This PR implements critical context caching and TPM optimizations for Gemini on OpenCode.

• Gold Prefix Optimization: Refactored hook_session_start.py to isolate a stable "Frozen Zone" (Identity, Mandates) from dynamic "Churn Zone" (Date, Memory). This ensures the context prefix remains bit-for-bit identical across sessions, maximizing cache hits.
• Subagent Cache Inheritance: Updated sync-agents-to-opencode.py to bake the Frozen Zone into every generated SKILL.md. Now subagents share the same prefix as the main session, starting with a "Warm Cache" instead of cold.
• TPM Protection: Forced model: flash for high-volume implementation agents (modular-builder, test-coverage, etc.) in OpenCode generation to prevent "Pro" model rate limit exhaustion during parallel dispatch.

Test Plan

• Verified hook_session_start.py outputs Frozen Zone first and Churn Zone last.
• Verified sync-agents-to-opencode.py injects Frozen Zone into generated skills.
• Verified modular-builder skill maps to flash model.
• Confirmed dynamic content (Date, Platform) appears only at the end of the prompt.

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[psklarkins]

Review: feat(gemini): optimize context caching and TPM usage

Verdict: Request Changes — Good concept, needs cleanup before merge.

What Works Well

• Frozen/Churn Zone separation is architecturally sound for Gemini prefix caching
• Defensive error handling improvements (stdin read, JSON parse, empty input) benefit both platforms
• seen_ids refactoring — DRY improvement, calculated once instead of twice
• memories_loaded simplification — cleaner calculation
• No Claude Code regressions — the else: branch is functionally equivalent to current main

Issues to Address

1. Memory rendering logic duplicated (High)
The identical ~24-line block (search_results iteration + unique_recent iteration) is copy-pasted into both the if IS_OPENCODE: and else: branches of hook_session_start.py. The only differences are heading levels and section titles. This violates DRY and creates a maintenance liability — any future change to memory formatting must be applied in two places.

Fix: Extract a shared helper function:

def format_memories(search_results, unique_recent, heading_level="###"):
    parts = []
    if search_results:
        parts.append(f"{heading_level} Relevant Memories")
        for result in search_results[:3]:
            parts.append(f"- **{result.memory.category}** (relevance: {result.score:.2f}): {result.memory.content}")
    if unique_recent:
        parts.append(f"\n{heading_level} Recent Context")
        for mem in unique_recent[:2]:
            parts.append(f"- {mem.category}: {mem.content}")
    return parts

Both branches call this with different heading levels. Single source of truth.

2. Session environment block also duplicated (Low)
The 3 lines formatting date/platform/cwd appear identically in both branches. Same fix pattern — extract or share.

3. frozen_header.md needs purpose comment (Medium)
The file contains OpenCode-specific identity text ("You are opencode...") in the shared repo. It's functionally gated (only read inside if IS_OPENCODE:), but should include a comment header explaining this:

<!-- OpenCode/Gemini only: Stable prefix for context caching.
     Read by hook_session_start.py inside IS_OPENCODE guard.
     Not used on Claude Code. -->

4. Plan doc references machine-specific paths (Low)
docs/superpowers/plans/2026-02-16-gemini-optimization-plan.md references C:/Przemek/ and C:/Users/biuro/ throughout. For an upstream PR, these should be relative paths or clearly noted as OpenCode-machine-specific.

Summary

The Frozen Zone / Churn Zone architecture is well-motivated. The defensive improvements are welcome. Fix the code duplication (extract shared helpers) and add context comments to the Gemini-only files, and this is good to merge.

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[psklarkins]

Changes Implemented

Addressed all review feedback:

1. DRY Fix in hook_session_start.py: Extracted format_memories and format_session_env helpers to eliminate duplication between branches.
2. Context Comment: Added purpose comment to .claude/context/frozen_header.md explaining it's only used for OpenCode caching.
3. Path Fixes: Updated plan document to use relative paths instead of hardcoded machine paths.

Ready for re-review.

[psklarkins]

Re-Review: commit 9281231 addresses all feedback

All 4 findings from the initial review have been addressed:

#	Finding	Status
1	Memory rendering duplicated	Fixed — extracted format_memories() helper with base_heading_level param. Both branches now call it (Gemini: level 3, Claude Code: level 2). Single source of truth.
2	Session environment duplicated	Fixed — extracted format_session_env() helper. Both branches use context_parts.extend(format_session_env()).
3	frozen_header.md needs purpose comment	Fixed — HTML comment added: "OpenCode/Gemini only: Stable prefix for context caching. Read by hook_session_start.py inside IS_OPENCODE guard. Not used on Claude Code."
4	Plan doc machine-specific paths	Fixed — C:/Przemek/ paths replaced with relative ./ paths, C:/Users/biuro/ replaced with ${OPENCODE_SKILLS_DIR}.

Verification

• Python AST parse: compiles cleanly
• Claude Code path: memories first (h2/h3), then "Session Environment" — unchanged behavior
• Gemini path: Frozen Zone header, then Churn Zone with session env + memories (h3/h4) — correct structure
• Helper functions are clean, minimal, and well-parameterized

Verdict: APPROVE — Ready to merge.

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