feat(sessions): named persistent sessions with resume (L1) (#22, #23)

- task schema: optional session (named id) -> persistent session dir at
  dataRoot/sessions/<name>, isolated per name
- pi adapter: --session-dir when declared (ephemeral --no-session stays
  the default otherwise); -c resumes the most recent session when present
- compose passthrough; result.json records session
- fixtures: tasks/session-demo-1.json (teach) + session-demo-2.json (recall)
- E2E: teach -> REMEMBERED + host-side session JSONL; resume -> recalled
  'mosaico' exactly; single continued session file

Closes #22, closes #23

adapters/pi/adapter.sh

@@ -18,6 +18,18 @@ if [ -n "${MOSAIC_WORKSPACE:-}" ]; then
     cd "$MOSAIC_WORKSPACE"
 fi
 
+# Session (M6): persistent named session directory; resume the most recent
+# session in that directory when one exists (pi documented flags).
+# Default remains ephemeral (--no-session) when no session is declared.
+SESSION_FLAGS="--no-session"
+if [ -n "${MOSAIC_SESSION_DIR:-}" ]; then
+    mkdir -p "$MOSAIC_SESSION_DIR"
+    SESSION_FLAGS="--session-dir $MOSAIC_SESSION_DIR"
+    if [ -n "$(ls -A "$MOSAIC_SESSION_DIR" 2>/dev/null)" ]; then
+        SESSION_FLAGS="$SESSION_FLAGS -c"
+    fi
+fi
+
 # Capabilities (M5): explicit allowlist or no tools.
 TOOLS_FLAG="--no-tools"
 [ -n "${MOSAIC_TOOLS:-}" ] && TOOLS_FLAG="--tools $MOSAIC_TOOLS"
@@ -30,13 +42,13 @@ TOOLS_FLAG="--no-tools"
 #   --offline      no startup network operations (update checks/telemetry)
 exec pi \
     --offline \
-    --no-session \
     --no-extensions \
     --no-skills \
     --no-prompt-templates \
     --no-themes \
     --no-context-files \
     $TOOLS_FLAG \
+    $SESSION_FLAGS \
     --provider "$PI_PROVIDER" \
     --model "$PI_MODEL" \
     --system-prompt "$(cat "$MOSAIC_SYSTEM_PROMPT_FILE")" \

compose.yaml

@@ -18,6 +18,8 @@ services:
       # Workspace + capabilities (set by the task runner; M5)
       MOSAIC_WORKSPACE: ${MOSAIC_WORKSPACE:-}
       MOSAIC_TOOLS: ${MOSAIC_TOOLS:-}
+      # Persistent named session dir (set by the task runner; M6)
+      MOSAIC_SESSION_DIR: ${MOSAIC_SESSION_DIR:-}
       # mock adapter only: verbatim response for deterministic seam tests
       MOSAIC_MOCK_RESPONSE: ${MOSAIC_MOCK_RESPONSE:-}
       # Documented container auth alternative: provider API key via

scripts/mosaic-task.mjs

@@ -106,7 +106,7 @@ function validateMission(document, file) {
 
 function validateTask(document, file) {
   if (!isPlainObject(document)) fail(2, "task must be a JSON object");
-  rejectUnknownKeys(document, ["taskVersion", "id", "prompt", "mission", "expectExact", "timeoutSeconds", "workspace", "capabilities"], "task");
+  rejectUnknownKeys(document, ["taskVersion", "id", "prompt", "mission", "expectExact", "timeoutSeconds", "workspace", "capabilities", "session"], "task");
   if (document.taskVersion !== 1) {
     fail(2, `unsupported taskVersion: ${JSON.stringify(document.taskVersion)} (supported: 1)`);
   }
@@ -158,6 +158,17 @@ function validateTask(document, file) {
     workspace = document.workspace;
   }
 
+  // Session (M6): optional named persistent session under
+  // <dataRoot>/sessions/<name>. Distinct names never share state.
+  let session = null;
+  if (document.session !== undefined && document.session !== null) {
+    if (typeof document.session !== "string" || document.session.length === 0) {
+      fail(2, 'task "session" must be a non-empty string when present');
+    }
+    validateId(document.session, "task session");
+    session = document.session;
+  }
+
   // Capabilities (M5): optional tools allowlist mapped by adapters to their
   // native permission flags. Absent = no tools.
   let tools = null;
@@ -189,6 +200,7 @@ function validateTask(document, file) {
     timeoutSeconds,
     workspace,
     tools,
+    session,
   };
 }
 
@@ -271,6 +283,12 @@ function runTask(taskFile) {
   if (workspaceContainerPath) spawnEnv.MOSAIC_WORKSPACE = workspaceContainerPath;
   spawnEnv.MOSAIC_TOOLS = task.tools ? task.tools.join(",") : "";
 
+  // Session (M6): persistent named session dir, passed as container path.
+  if (task.session) {
+    fs.mkdirSync(path.join(resolved.dataRoot, "sessions", task.session), { recursive: true });
+    spawnEnv.MOSAIC_SESSION_DIR = `/var/lib/mosaic/sessions/${task.session}`;
+  }
+
   const proc = spawnSync(
     "docker",
     ["compose", "run", "--rm", "-T", "mosaic-agent", task.prompt],
@@ -319,6 +337,7 @@ function runTask(taskFile) {
     expectedExact: expected,
     workspace: task.workspace,
     tools: task.tools,
+    session: task.session,
     exitCode: proc.status,
     signal: proc.signal ?? null,
     provider: resolved.execution.provider,

tasks/session-demo-1.json

@@ -0,0 +1,8 @@
+{
+  "taskVersion": 1,
+  "id": "t-session-teach",
+  "prompt": "Remember this code word for later: mosaico. Reply with exactly: REMEMBERED",
+  "session": "demo",
+  "expectExact": "REMEMBERED",
+  "timeoutSeconds": 180
+}

tasks/session-demo-2.json

@@ -0,0 +1,7 @@
+{
+  "taskVersion": 1,
+  "id": "t-session-recall",
+  "prompt": "What code word did I ask you to remember earlier in this session? Reply with only the code word.",
+  "session": "demo",
+  "timeoutSeconds": 180
+}