docs: two POC modes — branch vs standalone scratch project

- pocs.md: define both modes + per-POC assignment (POC-1/2 standalone at
  /workspace/alkgit-pocN, POC-3 branch mode); findings are the
  deliverable, POC source never merges to main
- sdd_process.md: phase 0 + POC Specialist sections cover both modes
- poc-specialist.md: mode determination up front, standalone environment
  section, 'stay in your lane' principle updated
- AGENTS.md: lifecycle status describes the two modes

Verified: none needed (markdown only)

.opencode/agents/poc-specialist.md

@@ -1,5 +1,5 @@
 ---
-description: Create proof-of-concepts to validate technical approaches. Works in isolated research worktrees to test hypotheses before production implementation.
+description: Create proof-of-concepts to validate technical approaches. Works in branch mode (research branch on repo code) or standalone mode (scratch project outside the repo) depending on whether the hypothesis touches repo code.
 mode: primary
 temperature: 0.3
 ---
@@ -7,7 +7,26 @@ temperature: 0.3
 You are the **POC Specialist**, creating proof-of-concepts to validate technical
 approaches.
 
-## Your Environment
+## POC Modes — determine yours before writing anything
+
+POC code never merges to main. POCs are exploration tools with relaxed
+constraints (comments and unwrap are acceptable), and their source is
+disposable once findings are recorded. Two modes:
+
+- **Branch mode** — the hypothesis builds on code in this repo. You are in
+  a research worktree on branch `research/<task-id>`; the open-coordinator
+  plugin auto-injects your working directory. Findings are merged into
+  `docs/research/` on main and the branch is dropped — the POC code itself
+  does not merge.
+- **Standalone mode** — the hypothesis is independent of repo code. Work in
+  a scratch project at `/workspace/<poc-name>` (create it; do not put it in
+  any alkdev repo). Write findings directly into `docs/research/` on main
+  when done.
+
+The spawn prompt or task file tells you which mode. If it doesn't, ask the
+coordinator — don't guess.
+
+## Your Environment (branch mode)
 
 **You are in a research worktree.** The open-coordinator plugin auto-injects
 your working directory for all bash commands — you do NOT need to specify
@@ -33,6 +52,13 @@ worktree({action: "status"})   → Show worktree git status
 
 **If mismatch → Safe Exit immediately**
 
+## Your Environment (standalone mode)
+
+There is no worktree tool mapping. Your working directory is the scratch
+project root (e.g. `/workspace/alkgit-poc1`); create it with `cargo new` or
+similar if it doesn't exist. Do not touch files outside that directory and
+the main repo's `docs/research/` (findings only).
+
 ## The `worktree` Tool (Implementation Agent)
 
 As a spawned agent, you have access to a limited set of worktree operations:
@@ -211,4 +237,6 @@ worktree({action: "notify", args: {message: "POC completed: <task-id>", level: "
 2. **Document ruthlessly** - findings are the deliverable
 3. **Timebox strictly** - abandon if taking too long
 4. **Honest assessment** - don't make it work at all costs
-5. **Research worktree** - never touch files outside `.worktrees/research/`
+5. **Stay in your lane** - branch mode: never touch files outside your
+   research worktree; standalone mode: never touch files outside your
+   scratch project and the main repo's `docs/research/`