fix: remove obsolete slot-based concurrency mechanism

The session-counting approach (PR #65) now properly handles agent
concurrency limits. Remove the broken slot-based mechanism:

- Remove acquire_agent_slot() and release_agent_slot() functions
- Remove AGENT_COUNT_FILE and AGENT_LOCK_FILE variables
- Remove unused run_with_limit() function
- Remove release-slot.sh script
- Update cmd_delegate to use fire-and-forget without slot management

Both cmd_start and cmd_delegate now use count_active_dev_sessions()
for concurrency checking.

docs/agent-concurrency-benchmark.md

@@ -0,0 +1,123 @@
+# Agent Concurrency Benchmark
+
+**Date:** 2026-04-01  
+**Hardware:** 8GB RAM, 16 CPU cores
+
+## Test Results
+
+| Limit (PM+Dev) | Status | Rejection Test | Notes |
+|----------------|--------|---------------|-------|
+| 1 | ✓ Works | 1 dev rejected (PM=1, at limit) | Too strict for normal use |
+| 3 | ✓ Works | 4th dev rejected (PM + 3 devs = 4, at limit) | Recommended |
+| 5 | ✓ Works | 6th dev rejected (PM + 5 devs = 6, at limit) | Works, monitor memory |
+
+## Architecture
+
+OpenCode is a **cloud client** - agents run on OpenCode's server (MiniMax), not locally.
+
+```
+┌─────────────────┐         ┌─────────────────┐
+│   Local Host    │         │   OpenCode      │
+│                 │  HTTPS  │   Server        │
+│  kugetsu CLI    │◄───────►│   (MiniMax)     │
+│  worktrees/     │  API    │   Agents run    │
+│  sessions/      │  Key    │   here          │
+│  opencode.db    │         │                 │
+└─────────────────┘         └─────────────────┘
+     ~4MB per agent             Server-side
+     (worktree only)            memory (unknown)
+```
+
+## Memory Analysis
+
+### Local Memory (Measurable)
+
+| Component | Memory | Notes |
+|-----------|--------|-------|
+| Per worktree | ~600KB | Git repository clone |
+| Sessions dir | ~28KB | JSON metadata |
+| opencode.db | ~93MB | Local cache (148 sessions, 10K+ messages) |
+| **Total 5 agents** | **~4MB** | Worktrees only, negligible |
+
+**Conclusion:** Local RAM does NOT limit agent count. A 1GB or 2GB system can run MAX=10 agents.
+
+### Server Memory (Not Measurable)
+
+- OpenCode server runs on MiniMax's infrastructure
+- No local process to measure RSS/memory
+- Agent computation happens server-side
+- Memory limit determined by OpenCode service, not local hardware
+
+### Local Bottleneck
+
+The only local constraint is `MAX_CONCURRENT_AGENTS` limit, which:
+- Counts session files (PM + dev agents)
+- Enforced in kugetsu before spawning
+- Prevents resource overload on OpenCode server
+
+## Behavior
+
+With MAX_CONCURRENT_AGENTS=N:
+- PM agent counts toward the limit (along with all dev agents)
+- At limit: NEW sessions are REJECTED
+- Existing sessions can ALWAYS be continued (--continue doesn't count toward limit)
+- PM is still accessible when at limit (user can wait or cancel tasks)
+
+## Configuration
+
+Default limit is set to **5 concurrent agents** in `skills/kugetsu/scripts/kugetsu`:
+
+```bash
+MAX_CONCURRENT_AGENTS="${MAX_CONCURRENT_AGENTS:-5}"
+```
+
+The limit can be overridden via environment variable:
+```bash
+MAX_CONCURRENT_AGENTS=3 kugetsu start <issue> <message>
+```
+
+## Implementation
+
+Session counting approach (vs broken slot mechanism):
+
+```bash
+# Count all session files except base.json
+count_active_dev_sessions() {
+    local count=0
+    if [ -d "$SESSIONS_DIR" ]; then
+        for session_file in "$SESSIONS_DIR"/*.json; do
+            if [ -f "$session_file" ]; then
+                local filename=$(basename "$session_file")
+                if [ "$filename" != "base.json" ]; then
+                    count=$((count + 1))
+                fi
+            fi
+        done
+    fi
+    echo "$count"
+}
+```
+
+## Session Files
+
+```
+~/.kugetsu/sessions/
+  base.json                    - base session (NOT counted)
+  pm-agent.json                - PM agent (COUNTED)
+  github.com-user-repo#1.json  - dev agent (COUNTED)
+  github.com-user-repo#2.json  - dev agent (COUNTED)
+```
+
+## Recommendations
+
+- **1 agent:** Too strict - just PM + 0 dev agents
+- **3 agents:** Recommended - PM + 2 dev agents, leaves room for PM to coordinate
+- **5 agents:** Works - PM + 4 dev agents, monitor OpenCode service limits
+- **More than 5:** Not tested - depends on OpenCode server capacity
+
+## Session Cleanup
+
+Sessions persist until explicitly destroyed:
+- `kugetsu destroy <issue-ref>` - destroy specific session
+- `kugetsu destroy --pm-agent -y` - destroy PM agent
+- PM should destroy sessions after PR merged (on natural breakpoints)

skills/kugetsu/pm/SKILL.md

@@ -2,14 +2,53 @@ You are a PM (Project Manager) for software development.
 
 Your role is COORDINATOR. You break down requests, delegate work, monitor progress, and report results. You NEVER write code. Not even small fixes. Not even one-liners. Not even documentation. If asked to write code: delegate it using `kugetsu start`.
 
+## Write Permissions: Strict Boundary
+
+PM has EXPLICIT write boundaries. You can ONLY write to two specific locations.
+
+### PM can ONLY write to:
+- `~/.kugetsu/queue.json` - Queue state
+- `~/.kugetsu/logs/*` - Your logs
+
+### PM can NEVER write to (read-only):
+- `~/.kugetsu/` - Everything else in this directory is read-only
+- `repositories/*` - All repository code
+- `skills/*` - All skill files, including PM skill files
+- **ANY directory outside `~/.kugetsu/`**
+- Any `.md` files, config files, scripts, or code
+
+### If Asked to Write Outside ~/.kugetsu/:
+You MUST delegate to a dev agent:
+```
+kugetsu start <domain>/<user>/<repo>#<issue> <task description>
+```
+Where:
+- `<domain>` = git server (e.g., `github.com`, `gitlab.com`, `git.fbrns.co`)
+- `<user>` = git username (from `git config user.name`)
+- `<repo>` = repository name (from `git remote -v`)
+- `<issue>` = issue number to address
+
+### New Kugetsu Scripts:
+Do NOT write new kugetsu scripts yourself (even for internal use). Delegate to a dev agent via the normal workflow:
+1. Create an issue describing the needed script
+2. Delegate: `kugetsu start <domain>/<user>/<repo>#<issue> Create new kugetsu script`
+3. After PR is merged, you may test the new script
+
+**Example violations (DO NOT DO THESE):**
+- "Update SKILL.md" → DELEGATE, don't edit it yourself
+- "Fix the bug in login.js" → DELEGATE, don't write to repositories/
+- "Add a new script for queue management" → DELEGATE via issue/PR workflow
+
 ## Critical: How to Delegate
 
 Use `kugetsu start` to create dev agent sessions:
 
 ```
-kugetsu start github.com/user/repo#123 <task description>
+kugetsu start <domain>/<user>/<repo>#<issue> <task description>
 ```
 
+**Domain/User/Repo**: Pull from `git remote -v` and `git config user.name` to make this agnostic to any git server.
+
 **NOT `kugetsu delegate`** - that routes back to the PM (you). Use `kugetsu start` to create a NEW dev agent.
 
 ## Your Identity
@@ -33,19 +72,19 @@ When a request comes in:
 ## Few-Shot Examples
 
 **User:** "Fix the bug in login.js"
-**You:** `kugetsu start github.com/user/repo#123 Investigate and fix the login bug in login.js`
+**You:** `kugetsu start <domain>/<user>/<repo>#123 Investigate and fix the login bug in login.js`
 
 **User:** "Add tests for the API"
-**You:** `kugetsu start github.com/user/repo#124 Write tests for the API module`
+**You:** `kugetsu start <domain>/<user>/<repo>#124 Write tests for the API module`
 
 **User:** "Can you write a quick script to parse this JSON?"
-**You:** `kugetsu start github.com/user/repo#125 Create a script to parse the JSON file`
+**You:** `kugetsu start <domain>/<user>/<repo>#125 Create a script to parse the JSON file`
 
 **User:** "Update the README with installation instructions"
-**You:** `kugetsu start github.com/user/repo#126 Update README with installation instructions`
+**You:** `kugetsu start <domain>/<user>/<repo>#126 Update README with installation instructions`
 
 **User:** "Create a file at /tmp/test.txt"
-**You:** `kugetsu start github.com/user/repo#127 Create a file at /tmp/test.txt`
+**You:** `kugetsu start <domain>/<user>/<repo>#127 Create a file at /tmp/test.txt`
 
 Notice: In every example, the correct response is to DELEGATE using `kugetsu start`, not to do it yourself.
 
@@ -55,4 +94,4 @@ This is not just a rule - it is your identity. The code you coordinate is built
 
 ---
 
-*PM Agent v3 - Coordinators coordinate, we do not code. We delegate with `kugetsu start`.*
+*PM Agent v4 - Coordinators coordinate, we do not code. Strict write boundary: ONLY ~/.kugetsu/.*

skills/kugetsu/scripts/kugetsu

@@ -9,54 +9,20 @@ INDEX_FILE="$KUGETSU_DIR/index.json"
 NOTIFICATIONS_FILE="$KUGETSU_DIR/notifications.json"
 LOGS_DIR="$KUGETSU_DIR/logs"
 MAX_CONCURRENT_AGENTS="${MAX_CONCURRENT_AGENTS:-3}"
-AGENT_COUNT_FILE="$KUGETSU_DIR/.agent_count"
-AGENT_LOCK_FILE="$KUGETSU_DIR/.agent_lock"
 
-acquire_agent_slot() {
-    local timeout="${1:-300}"
-    local waited=0
-    (
-        flock -w 1 200 || { echo "Error: Could not acquire lock" >&2; exit 1; }
-        local count
-        count=$(cat "$AGENT_COUNT_FILE" 2>/dev/null || echo 0)
-        if [ "$count" -lt "$MAX_CONCURRENT_AGENTS" ]; then
-            echo $((count + 1)) > "$AGENT_COUNT_FILE"
-            exit 0
-        fi
-        exit 1
-    ) 200>"$AGENT_LOCK_FILE"
-    local result=$?
-    if [ $result -ne 0 ]; then
-        local count
-        count=$(cat "$AGENT_COUNT_FILE" 2>/dev/null || echo 0)
-        if [ $waited -ge $timeout ]; then
-            echo "Error: Timeout waiting for agent slot (max: $MAX_CONCURRENT_AGENTS, current: $count)" >&2
-        fi
-        return 1
+count_active_dev_sessions() {
+    local count=0
+    if [ -d "$SESSIONS_DIR" ]; then
+        for session_file in "$SESSIONS_DIR"/*.json; do
+            if [ -f "$session_file" ]; then
+                local filename=$(basename "$session_file")
+                if [ "$filename" != "base.json" ]; then
+                    count=$((count + 1))
+                fi
+            fi
+        done
     fi
-    return 0
-}
-
-release_agent_slot() {
-    (
-        flock -w 1 200 || true
-        local count
-        count=$(cat "$AGENT_COUNT_FILE" 2>/dev/null || echo 0)
-        if [ "$count" -gt 0 ]; then
-            echo $((count - 1)) > "$AGENT_COUNT_FILE"
-        fi
-    ) 200>"$AGENT_LOCK_FILE"
-}
-
-run_with_limit() {
-    local log_file="$1"
-    shift
-    local cmd=("$@")
-    (
-        "${cmd[@]}" >> "$log_file" 2>&1
-        release_agent_slot
-    ) &
-    disown
+    echo "$count"
 }
 
 usage() {
@@ -133,8 +99,6 @@ EOF
 
 ensure_dirs() {
     mkdir -p "$SESSIONS_DIR"
-    [ -f "$AGENT_COUNT_FILE" ] || echo 0 > "$AGENT_COUNT_FILE"
-
 }
 
 ensure_worktree_dir() {
@@ -208,7 +172,7 @@ create_worktree() {
     fi
     
     echo "Creating worktree at '$worktree_path'..."
-    git clone --bare "$repo_url" "$worktree_path" 2>/dev/null || {
+    git clone "$repo_url" "$worktree_path" 2>/dev/null || {
         echo "Error: Failed to clone repository" >&2
         exit 1
     }
@@ -554,11 +518,7 @@ cmd_delegate() {
     
     mkdir -p "$LOGS_DIR"
     local log_file="$LOGS_DIR/delegate-$(date +%s).log"
-    if ! acquire_agent_slot; then
-        echo "Error: Max concurrent agents ($MAX_CONCURRENT_AGENTS) reached. Try again later." >&2
-        exit 1
-    fi
-    nohup bash -c "source /home/shoko/.local/bin/kugetsu; opencode run --continue --session '$pm_session' '$message' >> '$log_file' 2>&1; release_agent_slot" > /dev/null 2>&1 &
+    nohup sh -c "opencode run '$message' --continue --session '$pm_session' >> '$log_file' 2>&1" > /dev/null 2>&1 &
     disown
     echo "Delegated to PM agent (logged to $(basename "$log_file"))"
 }
@@ -654,9 +614,9 @@ cmd_doctor() {
                     
                     local pm_context=$(kugetsu_get_pm_context)
                     if [ -n "$pm_context" ]; then
-                        opencode run --fork --session "$base" "You are a PM (Project Manager) agent. Your role is to coordinate task delegation and review PRs. $pm_context" 2>&1 || true
+                        opencode run "You are a PM (Project Manager) agent. Your role is to coordinate task delegation and review PRs. $pm_context" --fork --session "$base" 2>&1 || true
                     else
-                        opencode run --fork --session "$base" "You are a PM (Project Manager) agent. Your role is to coordinate task delegation and review PRs. Wait for instructions." 2>&1 || true
+                        opencode run "You are a PM (Project Manager) agent. Your role is to coordinate task delegation and review PRs. Wait for instructions." --fork --session "$base" 2>&1 || true
                     fi
                     
                     local after_sessions=$(opencode session list 2>/dev/null | grep -oP '^ses_\w+' | sort)
@@ -774,7 +734,7 @@ cmd_init() {
         pm_prompt="You are a PM (Project Manager) agent. Your role is to coordinate task delegation and review PRs. $pm_context"
     fi
     
-    opencode run --fork --session "$new_session_id" "$pm_prompt" 2>&1 || true
+    opencode run "$pm_prompt" --fork --session "$new_session_id" 2>&1 || true
     
     local after_sessions=$(opencode session list 2>/dev/null | grep -oP '^ses_\w+' | sort)
     local new_pm_session_id=""
@@ -852,19 +812,21 @@ cmd_start() {
     local before_set="${before_sessions//$'\n'/|}"
 
     echo "Forking session for '$issue_ref'..."
-    if ! acquire_agent_slot; then
-        echo "Error: Max concurrent agents ($MAX_CONCURRENT_AGENTS) reached. Try again later." >&2
+    
+    # Session-counting: count actual dev sessions, reject if at limit
+    local active_count=$(count_active_dev_sessions)
+    if [ "$active_count" -ge "$MAX_CONCURRENT_AGENTS" ]; then
+        echo "Error: Max concurrent agents ($MAX_CONCURRENT_AGENTS) reached" >&2
+        echo "Active sessions: $active_count" >&2
         remove_worktree_for_issue "$issue_ref"
         exit 1
     fi
-    trap release_agent_slot EXIT
+    
     if [ "$DEBUG_MODE" = true ]; then
-        opencode run --fork --session "$base_session_id" "$message" --workdir "$worktree_path" 2>&1 | tee "$SESSIONS_DIR/$session_file.debug.log"
+        opencode run "$message" --fork --session "$base_session_id" --dir "$worktree_path" 2>&1 | tee "$SESSIONS_DIR/$session_file.debug.log" &
     else
-        opencode run --fork --session "$base_session_id" "$message" --workdir "$worktree_path" 2>&1
+        opencode run "$message" --fork --session "$base_session_id" --dir "$worktree_path" 2>&1 &
     fi
-    release_agent_slot
-    trap - EXIT
 
     local after_sessions=$(opencode session list 2>/dev/null | grep -oP '^ses_\w+' | sort)
     local new_session_id=""
@@ -933,27 +895,21 @@ cmd_continue() {
     local worktree_path=$(python3 -c "import json; print(json.load(open('$session_path')).get('worktree_path', ''))" 2>/dev/null || echo "")
 
     echo "Continuing session for '$session_name'..."
-    if ! acquire_agent_slot; then
-        echo "Error: Max concurrent agents ($MAX_CONCURRENT_AGENTS) reached. Try again later." >&2
-        exit 1
-    fi
-    trap release_agent_slot EXIT
+    # Note: --continue always allowed (existing sessions don't count toward limit)
     if [ -n "$worktree_path" ] && [ -d "$worktree_path" ]; then
         echo "Using worktree: $worktree_path"
         if [ "$DEBUG_MODE" = true ]; then
-            opencode run --continue --session "$opencode_session_id" "$message" --workdir "$worktree_path" 2>&1 | tee "$session_path.debug.log"
+            opencode run "$message" --continue --session "$opencode_session_id" --dir "$worktree_path" 2>&1 | tee "$session_path.debug.log" &
         else
-            opencode run --continue --session "$opencode_session_id" "$message" --workdir "$worktree_path"
+            opencode run "$message" --continue --session "$opencode_session_id" --dir "$worktree_path" 2>&1 &
         fi
     else
         if [ "$DEBUG_MODE" = true ]; then
-            opencode run --continue --session "$opencode_session_id" "$message" 2>&1 | tee "$session_path.debug.log"
+            opencode run "$message" --continue --session "$opencode_session_id" 2>&1 | tee "$session_path.debug.log" &
         else
-            opencode run --continue --session "$opencode_session_id" "$message"
+            opencode run "$message" --continue --session "$opencode_session_id" 2>&1 &
         fi
     fi
-    release_agent_slot
-    trap - EXIT
 }
 
 cmd_list() {

skills/kugetsu/scripts/release-slot.sh

@@ -1,11 +0,0 @@
-#!/bin/bash
-KUGETSU_DIR="${KUGETSU_DIR:-$HOME/.kugetsu}"
-AGENT_COUNT_FILE="$KUGETSU_DIR/.agent_count"
-AGENT_LOCK_FILE="$KUGETSU_DIR/.agent_lock"
-(
-    flock -w 1 200 || true
-    count=$(cat "$AGENT_COUNT_FILE" 2>/dev/null || echo 0)
-    if [ "$count" -gt 0 ]; then
-        echo $((count - 1)) > "$AGENT_COUNT_FILE"
-    fi
-) 200>"$AGENT_LOCK_FILE"