fix: sync spike/sketch workflows with upstream skill v2 improvements

Spike workflow:
- Add frontier mode (no-arg or "frontier" proposes integration + frontier spikes)
- Add depth-over-speed principle — follow surprising findings, test edge cases,
  document investigation trail not just verdict
- Add CONVENTIONS.md awareness — follow established patterns, update after session
- Add Requirements section in MANIFEST — track design decisions as they emerge
- Add re-ground step before each spike to prevent drift in long sessions
- Add Investigation Trail section to README template
- Restructured prior context loading with priority ordering
- Research step now runs per-spike with briefing and approach comparison table

Sketch workflow:
- Add frontier mode (no-arg or "frontier" proposes consistency + frontier sketches)
- Add spike context loading — ground mockups in real data shapes, requirements,
  and conventions from spike findings

Spike wrap-up workflow:
- Add CONVENTIONS.md generation step (recurring stack/structure/pattern choices)
- Reference files now use implementation blueprint format (Requirements, How to
  Build It, What to Avoid, Constraints)
- SKILL.md now includes requirements section from MANIFEST
- Next-steps route to /gsd-spike frontier mode instead of inline analysis

Sketch wrap-up workflow:
- Next-steps route to /gsd-sketch frontier mode

Commands updated with frontier mode in descriptions and argument hints.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

commands/gsd/sketch.md

@@ -1,7 +1,7 @@
 ---
 name: gsd:sketch
-description: Rapidly sketch UI/design ideas using throwaway HTML mockups with multi-variant exploration
-argument-hint: "<design idea to explore> [--quick]"
+description: Sketch UI/design ideas with throwaway HTML mockups, or propose what to sketch next (frontier mode)
+argument-hint: "[design idea to explore] [--quick] [--text] or [frontier]"
 allowed-tools:
   - Read
   - Write
@@ -10,11 +10,20 @@ allowed-tools:
   - Grep
   - Glob
   - AskUserQuestion
+  - WebSearch
+  - WebFetch
+  - mcp__context7__resolve-library-id
+  - mcp__context7__query-docs
 ---
 <objective>
 Explore design directions through throwaway HTML mockups before committing to implementation.
 Each sketch produces 2-3 variants for comparison. Sketches live in `.planning/sketches/` and
-integrate with GSD commit patterns, state tracking, and handoff workflows.
+integrate with GSD commit patterns, state tracking, and handoff workflows. Loads spike
+findings to ground mockups in real data shapes and validated interaction patterns.
+
+Two modes:
+- **Idea mode** (default) — describe a design idea to sketch
+- **Frontier mode** (no argument or "frontier") — analyzes existing sketch landscape and proposes consistency and frontier sketches
 
 Does not require `/gsd-new-project` — auto-creates `.planning/sketches/` if needed.
 </objective>
@@ -41,5 +50,5 @@ Design idea: $ARGUMENTS
 
 <process>
 Execute the sketch workflow from @~/.claude/get-shit-done/workflows/sketch.md end-to-end.
-Preserve all workflow gates (intake, decomposition, variant evaluation, MANIFEST updates, commit patterns).
+Preserve all workflow gates (intake, decomposition, target stack research, variant evaluation, MANIFEST updates, commit patterns).
 </process>

commands/gsd/spike.md

@@ -1,7 +1,7 @@
 ---
 name: gsd:spike
-description: Rapidly spike an idea with throwaway experiments to validate feasibility before planning
-argument-hint: "<idea to validate> [--quick]"
+description: Spike an idea through experiential exploration, or propose what to spike next (frontier mode)
+argument-hint: "[idea to validate] [--quick] [--text] or [frontier]"
 allowed-tools:
   - Read
   - Write
@@ -10,11 +10,20 @@ allowed-tools:
   - Grep
   - Glob
   - AskUserQuestion
+  - WebSearch
+  - WebFetch
+  - mcp__context7__resolve-library-id
+  - mcp__context7__query-docs
 ---
 <objective>
-Rapid feasibility validation through focused, throwaway experiments. Each spike answers one
-specific question with observable evidence. Spikes live in `.planning/spikes/` and integrate
-with GSD commit patterns, state tracking, and handoff workflows.
+Spike an idea through experiential exploration — build focused experiments to feel the pieces
+of a future app, validate feasibility, and produce verified knowledge for the real build.
+Spikes live in `.planning/spikes/` and integrate with GSD commit patterns, state tracking,
+and handoff workflows.
+
+Two modes:
+- **Idea mode** (default) — describe an idea to spike
+- **Frontier mode** (no argument or "frontier") — analyzes existing spike landscape and proposes integration and frontier spikes
 
 Does not require `/gsd-new-project` — auto-creates `.planning/spikes/` if needed.
 </objective>
@@ -33,9 +42,10 @@ Idea: $ARGUMENTS
 
 **Available flags:**
 - `--quick` — Skip decomposition/alignment, jump straight to building. Use when you already know what to spike.
+- `--text` — Use plain-text numbered lists instead of AskUserQuestion (for non-Claude runtimes).
 </context>
 
 <process>
 Execute the spike workflow from @~/.claude/get-shit-done/workflows/spike.md end-to-end.
-Preserve all workflow gates (decomposition, risk ordering, verification, MANIFEST updates, commit patterns).
+Preserve all workflow gates (prior spike check, decomposition, research, risk ordering, observability assessment, verification, MANIFEST updates, commit patterns).
 </process>