feat: add multi-runtime support (coord run, prdy --codex) and next-task capsule

- coord/prdy subcommands now accept --claude/--codex runtime flags
- New `mosaic coord run` generates continuation context and launches
  selected runtime, replacing manual copy/paste workflow
- Next-task capsule (.mosaic/orchestrator/next-task.json) provides
  machine-readable execution context for deterministic session launches
- Codex strict orchestrator profile added to runtime/codex/RUNTIME.md
- Orchestrator protocol updated with between-session run flow
- New smoke-test.sh for orchestration behavior verification

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tools/prdy/_lib.sh

@@ -41,6 +41,20 @@ _require_cmd() {
   fi
 }
 
+prdy_runtime() {
+  local runtime="${MOSAIC_PRDY_RUNTIME:-claude}"
+  case "$runtime" in
+    claude|codex) echo "$runtime" ;;
+    *) echo "claude" ;;
+  esac
+}
+
+prdy_runtime_command() {
+  local runtime
+  runtime="$(prdy_runtime)"
+  echo "$runtime"
+}
+
 # ─── PRD detection ───────────────────────────────────────────────────────────
 
 # Find the PRD file in a project directory.

tools/prdy/prdy-init.sh

@@ -1,12 +1,12 @@
 #!/usr/bin/env bash
 set -euo pipefail
 #
-# prdy-init.sh — Create a new PRD via guided Claude session
+# prdy-init.sh — Create a new PRD via guided runtime session
 #
 # Usage:
 #   prdy-init.sh [--project <path>] [--name <feature>]
 #
-# Launches a dedicated Claude Code session in yolo mode with a specialized
+# Launches a dedicated runtime session in yolo mode with a specialized
 # system prompt that guides the user through PRD creation. The output is
 # written to docs/PRD.md.
 
@@ -24,15 +24,15 @@ while [[ $# -gt 0 ]]; do
     --name)    NAME="$2"; shift 2 ;;
     -h|--help)
       cat <<'USAGE'
-prdy-init.sh — Create a new PRD via guided Claude session
+prdy-init.sh — Create a new PRD via guided runtime session
 
 Usage: prdy-init.sh [--project <path>] [--name <feature>]
 
 Options:
   --project <path>   Project directory (default: CWD)
-  --name <feature>   Feature or project name (optional, Claude will ask if omitted)
+  --name <feature>   Feature or project name (optional, runtime will ask if omitted)
 
-Launches Claude Code in yolo mode with a PRD-focused system prompt.
+Launches the selected runtime in yolo mode with a PRD-focused prompt.
 The agent will ask clarifying questions, then write docs/PRD.md.
 
 Examples:
@@ -51,7 +51,8 @@ PROJECT="${PROJECT/#\~/$HOME}"
 
 # ─── Preflight checks ───────────────────────────────────────────────────────
 
-_require_cmd "claude"
+RUNTIME_CMD="$(prdy_runtime_command)"
+_require_cmd "$RUNTIME_CMD"
 
 # Check for existing PRD
 EXISTING="$(find_prd "$PROJECT")"
@@ -77,11 +78,29 @@ else
   KICKOFF="Create docs/PRD.md for this project. Read the project context first, then ask the user what they want to build. Ask clarifying questions before writing the PRD."
 fi
 
-# ─── Launch Claude ───────────────────────────────────────────────────────────
+# ─── Launch runtime ──────────────────────────────────────────────────────────
 
 info "Output target: $PROJECT/$PRD_CANONICAL"
-info "Mode: PRD Creation (yolo)"
+info "Mode: PRD Creation (yolo, runtime: $RUNTIME_CMD)"
 echo ""
 
 cd "$PROJECT"
-exec claude --dangerously-skip-permissions --append-system-prompt "$SYSTEM_PROMPT" "$KICKOFF"
+if [[ "$RUNTIME_CMD" == "claude" ]]; then
+  exec claude --dangerously-skip-permissions --append-system-prompt "$SYSTEM_PROMPT" "$KICKOFF"
+fi
+
+if [[ "$RUNTIME_CMD" == "codex" ]]; then
+  CODEX_PROMPT="$(cat <<EOF
+Follow this PRD contract exactly.
+
+$SYSTEM_PROMPT
+
+Task:
+$KICKOFF
+EOF
+)"
+  exec codex --dangerously-bypass-approvals-and-sandbox "$CODEX_PROMPT"
+fi
+
+fail "Unsupported runtime: $RUNTIME_CMD"
+exit 1

tools/prdy/prdy-update.sh

@@ -1,12 +1,12 @@
 #!/usr/bin/env bash
 set -euo pipefail
 #
-# prdy-update.sh — Update an existing PRD via guided Claude session
+# prdy-update.sh — Update an existing PRD via guided runtime session
 #
 # Usage:
 #   prdy-update.sh [--project <path>]
 #
-# Launches a dedicated Claude Code session in yolo mode with a specialized
+# Launches a dedicated runtime session in yolo mode with a specialized
 # system prompt that reads the existing PRD and guides targeted modifications.
 
 SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
@@ -21,14 +21,14 @@ while [[ $# -gt 0 ]]; do
     --project) PROJECT="$2"; shift 2 ;;
     -h|--help)
       cat <<'USAGE'
-prdy-update.sh — Update an existing PRD via guided Claude session
+prdy-update.sh — Update an existing PRD via guided runtime session
 
 Usage: prdy-update.sh [--project <path>]
 
 Options:
   --project <path>   Project directory (default: CWD)
 
-Launches Claude Code in yolo mode with a PRD-update system prompt.
+Launches the selected runtime in yolo mode with a PRD-update prompt.
 The agent will read the existing docs/PRD.md, summarize its state,
 and ask what changes are needed.
 
@@ -47,7 +47,8 @@ PROJECT="${PROJECT/#\~/$HOME}"
 
 # ─── Preflight checks ───────────────────────────────────────────────────────
 
-_require_cmd "claude"
+RUNTIME_CMD="$(prdy_runtime_command)"
+_require_cmd "$RUNTIME_CMD"
 
 # Require existing PRD
 EXISTING="$(find_prd "$PROJECT")"
@@ -65,11 +66,29 @@ SYSTEM_PROMPT="$(build_prdy_system_prompt "update")"
 
 KICKOFF="Read the existing PRD at ${EXISTING}, summarize its current state, then ask what changes or additions are needed."
 
-# ─── Launch Claude ───────────────────────────────────────────────────────────
+# ─── Launch runtime ──────────────────────────────────────────────────────────
 
 info "Updating: $EXISTING"
-info "Mode: PRD Update (yolo)"
+info "Mode: PRD Update (yolo, runtime: $RUNTIME_CMD)"
 echo ""
 
 cd "$PROJECT"
-exec claude --dangerously-skip-permissions --append-system-prompt "$SYSTEM_PROMPT" "$KICKOFF"
+if [[ "$RUNTIME_CMD" == "claude" ]]; then
+  exec claude --dangerously-skip-permissions --append-system-prompt "$SYSTEM_PROMPT" "$KICKOFF"
+fi
+
+if [[ "$RUNTIME_CMD" == "codex" ]]; then
+  CODEX_PROMPT="$(cat <<EOF
+Follow this PRD contract exactly.
+
+$SYSTEM_PROMPT
+
+Task:
+$KICKOFF
+EOF
+)"
+  exec codex --dangerously-bypass-approvals-and-sandbox "$CODEX_PROMPT"
+fi
+
+fail "Unsupported runtime: $RUNTIME_CMD"
+exit 1