diff --git a/openspec/changes/agent-codex-codex-session-task-mode-decider-2026-04-22-12-16/.openspec.yaml b/openspec/changes/agent-codex-codex-session-task-mode-decider-2026-04-22-12-16/.openspec.yaml
new file mode 100644
index 0000000..25345f4
--- /dev/null
+++ b/openspec/changes/agent-codex-codex-session-task-mode-decider-2026-04-22-12-16/.openspec.yaml
@@ -0,0 +1,2 @@
+schema: spec-driven
+created: 2026-04-22
diff --git a/openspec/changes/agent-codex-codex-session-task-mode-decider-2026-04-22-12-16/proposal.md b/openspec/changes/agent-codex-codex-session-task-mode-decider-2026-04-22-12-16/proposal.md
new file mode 100644
index 0000000..35f18b5
--- /dev/null
+++ b/openspec/changes/agent-codex-codex-session-task-mode-decider-2026-04-22-12-16/proposal.md
@@ -0,0 +1,17 @@
+## Why
+
+- Guardex currently documents OpenSpec tiers on `gx branch start`, but the start script still treated tier selection as a no-op and always behaved like the full scaffold path once auto-bootstrap was enabled.
+- Codex launches also had no lightweight task-size gate, so tiny asks paid the full OMX/T3 setup cost even when the repo contract says those asks should stay caveman-only.
+- Active session records did not preserve the routing decision, which made takeover prompts and the Active Agents surface blind to whether a sandbox was intentionally lightweight or OMX-backed.
+
+## What Changes
+
+- Wire real `T0`/`T1`/`T2`/`T3` behavior into `scripts/agent-branch-start.sh` and its template so auto-bootstrapped branch starts create the right OpenSpec footprint for the requested tier.
+- Add a task-size decider to `scripts/codex-agent.sh` and its template so explicit lightweight asks route to caveman with `T1`, standard behavior changes route to OMX with `T2`, and orchestration-heavy asks escalate to `T3`.
+- Persist `taskMode`, `openspecTier`, and `taskRoutingReason` in the active-session record schema and cover the new behavior with focused branch-start, sandbox, and session-state tests.
+
+## Impact
+
+- Affected surfaces are the Guardex branch bootstrap path, Codex launcher flow, and the VS Code Active Agents session metadata readers.
+- Main risk is routing drift between the branch-start script, the Codex launcher, and the session schema; the targeted regression suite now exercises those surfaces together to keep them aligned.
+- Existing default `gx branch start` behavior remains intact when `GUARDEX_OPENSPEC_AUTO_INIT=false`; tiered scaffolding only materializes on the same auto-bootstrap path Guardex already uses when OpenSpec initialization is enabled.
diff --git a/openspec/changes/agent-codex-codex-session-task-mode-decider-2026-04-22-12-16/specs/codex-session-task-routing/spec.md b/openspec/changes/agent-codex-codex-session-task-mode-decider-2026-04-22-12-16/specs/codex-session-task-routing/spec.md
new file mode 100644
index 0000000..143e56e
--- /dev/null
+++ b/openspec/changes/agent-codex-codex-session-task-mode-decider-2026-04-22-12-16/specs/codex-session-task-routing/spec.md
@@ -0,0 +1,41 @@
+## ADDED Requirements
+
+### Requirement: Guardex branch start honors OpenSpec tiers
+`gx branch start` SHALL apply the requested OpenSpec tier instead of always creating the full T3 scaffold.
+
+#### Scenario: T1 branch start creates a notes-only change workspace
+- **WHEN** an operator runs `gx branch start --tier T1 ...`
+- **THEN** Guardex creates the agent branch/worktree
+- **AND** it initializes `openspec/changes/<change>/notes.md` plus `.openspec.yaml`
+- **AND** it does not create `proposal.md`, `tasks.md`, or an `openspec/plan/<plan>/` workspace.
+
+#### Scenario: T2 branch start skips the plan workspace
+- **WHEN** an operator runs `gx branch start --tier T2 ...`
+- **THEN** Guardex creates the full change workspace with `proposal.md`, `tasks.md`, and `specs/.../spec.md`
+- **AND** it does not create an `openspec/plan/<plan>/` workspace.
+
+#### Scenario: T3 branch start keeps the full scaffold
+- **WHEN** an operator runs `gx branch start --tier T3 ...`
+- **THEN** Guardex creates both the full change workspace and the plan workspace.
+
+### Requirement: Codex launcher auto-routes task size into mode plus tier
+The Codex launcher SHALL classify the requested task before starting the sandbox and choose the lightweight or OMX lane accordingly.
+
+#### Scenario: explicit lightweight task routes to caveman and T1
+- **WHEN** `scripts/codex-agent.sh` launches a task whose text starts with `quick:`, `simple:`, `tiny:`, `minor:`, `small:`, `just:`, or `only:`
+- **THEN** it reports a `caveman` task mode
+- **AND** it starts the sandbox with OpenSpec tier `T1`
+- **AND** the launched Codex process receives the selected mode/tier in its environment.
+
+#### Scenario: non-trivial task routes to OMX-backed tiers
+- **WHEN** `scripts/codex-agent.sh` launches a broader behavior/refactor/workflow task without a lightweight prefix
+- **THEN** it reports an `omx` task mode
+- **AND** it selects `T2` by default
+- **AND** it upgrades to `T3` for clearly plan-heavy or orchestration-heavy requests.
+
+### Requirement: active session records capture the routing decision
+The active session record written for Codex sandboxes SHALL preserve the selected task mode and OpenSpec tier.
+
+#### Scenario: active session record stores mode plus tier
+- **WHEN** `scripts/agent-session-state.js start ...` is called with task-routing metadata
+- **THEN** the written `.omx/state/active-sessions/*.json` record includes the selected task mode, OpenSpec tier, and routing reason.
diff --git a/openspec/changes/agent-codex-codex-session-task-mode-decider-2026-04-22-12-16/tasks.md b/openspec/changes/agent-codex-codex-session-task-mode-decider-2026-04-22-12-16/tasks.md
new file mode 100644
index 0000000..6799b3e
--- /dev/null
+++ b/openspec/changes/agent-codex-codex-session-task-mode-decider-2026-04-22-12-16/tasks.md
@@ -0,0 +1,36 @@
+## Definition of Done
+
+This change is complete only when **all** of the following are true:
+
+- Every checkbox below is checked.
+- The agent branch reaches `MERGED` state on `origin` and the PR URL + state are recorded in the completion handoff.
+- If any step blocks (test failure, conflict, ambiguous result), append a `BLOCKED:` line under section 4 explaining the blocker and **STOP**. Do not tick remaining cleanup boxes; do not silently skip the cleanup pipeline.
+
+## Handoff
+
+- Handoff: change=`agent-codex-codex-session-task-mode-decider-2026-04-22-12-16`; branch=`agent/codex/codex-session-task-mode-decider-2026-04-22-12-16`; scope=`scripts/agent-branch-start.sh, scripts/codex-agent.sh, scripts/agent-session-state.js, templates/scripts/agent-branch-start.sh, templates/scripts/codex-agent.sh, vscode/guardex-active-agents/session-schema.js, templates/vscode/guardex-active-agents/session-schema.js, test/branch.test.js, test/sandbox.test.js, test/vscode-active-agents-session-state.test.js, openspec/changes/agent-codex-codex-session-task-mode-decider-2026-04-22-12-16/*`; action=`finish the tier-aware branch-start and task-routing lane, verify the focused coverage, then run the mandatory PR merge + cleanup flow`.
+- Copy prompt: Continue `agent-codex-codex-session-task-mode-decider-2026-04-22-12-16` on branch `agent/codex/codex-session-task-mode-decider-2026-04-22-12-16`. Work inside the existing sandbox, review `openspec/changes/agent-codex-codex-session-task-mode-decider-2026-04-22-12-16/tasks.md`, continue from the current state instead of creating a new sandbox, and when the work is done run `gx branch finish --branch agent/codex/codex-session-task-mode-decider-2026-04-22-12-16 --base main --via-pr --wait-for-merge --cleanup`.
+
+## 1. Specification
+
+- [x] 1.1 Finalize proposal scope and acceptance criteria for `agent-codex-codex-session-task-mode-decider-2026-04-22-12-16`.
+- [x] 1.2 Define normative requirements in `specs/codex-session-task-routing/spec.md`.
+
+## 2. Implementation
+
+- [x] 2.1 Wire real `T0/T1/T2/T3` behavior into `scripts/agent-branch-start.sh` and `templates/scripts/agent-branch-start.sh`.
+- [x] 2.2 Add a Codex-side task-mode decider in `scripts/codex-agent.sh` and `templates/scripts/codex-agent.sh` so simple asks route to caveman/T1 and broader asks route to OMX/T2-or-T3.
+- [x] 2.3 Persist the selected task mode/tier in the active-session record surface.
+- [x] 2.4 Add/update focused regression coverage for branch-start tier scaffolding, codex-agent routing, and session metadata.
+
+## 3. Verification
+
+- [x] 3.1 Run targeted project verification commands. `node --test test/branch.test.js test/sandbox.test.js test/vscode-active-agents-session-state.test.js` passed after aligning the new tiered branch-start tests with the existing `GUARDEX_OPENSPEC_AUTO_INIT=true` bootstrap path; `git diff --check` also passed cleanly.
+- [x] 3.2 Run `openspec validate agent-codex-codex-session-task-mode-decider-2026-04-22-12-16 --type change --strict`. Result: `Change 'agent-codex-codex-session-task-mode-decider-2026-04-22-12-16' is valid`.
+- [x] 3.3 Run `openspec validate --specs`. Result: command completed successfully and reported `No items found to validate.`
+
+## 4. Cleanup (mandatory; run before claiming completion)
+
+- [ ] 4.1 Run the cleanup pipeline: `gx branch finish --branch agent/codex/codex-session-task-mode-decider-2026-04-22-12-16 --base main --via-pr --wait-for-merge --cleanup`. This handles commit -> push -> PR create -> merge wait -> worktree prune in one invocation.
+- [ ] 4.2 Record the PR URL and final merge state (`MERGED`) in the completion handoff.
+- [ ] 4.3 Confirm the sandbox worktree is gone (`git worktree list` no longer shows the agent path; `git branch -a` shows no surviving local/remote refs for the branch).
diff --git a/scripts/agent-branch-start.sh b/scripts/agent-branch-start.sh
index c871372..9da6d60 100755
--- a/scripts/agent-branch-start.sh
+++ b/scripts/agent-branch-start.sh
@@ -14,6 +14,7 @@ OPENSPEC_PLAN_SLUG_OVERRIDE="${GUARDEX_OPENSPEC_PLAN_SLUG:-}"
 OPENSPEC_CHANGE_SLUG_OVERRIDE="${GUARDEX_OPENSPEC_CHANGE_SLUG:-}"
 OPENSPEC_CAPABILITY_SLUG_OVERRIDE="${GUARDEX_OPENSPEC_CAPABILITY_SLUG:-}"
 OPENSPEC_MASTERPLAN_LABEL_RAW="${GUARDEX_OPENSPEC_MASTERPLAN_LABEL-masterplan}"
+OPENSPEC_TIER_RAW="${GUARDEX_OPENSPEC_TIER:-T3}"
 PRINT_NAME_ONLY=0
 POSITIONAL_ARGS=()
 
@@ -54,8 +55,7 @@ while [[ $# -gt 0 ]]; do
       shift
       ;;
     --tier)
-      # Accepted for CLAUDE.md compatibility; scaffold size is not yet wired
-      # through this script. Consume the value so callers can pass it.
+      OPENSPEC_TIER_RAW="${2:-$OPENSPEC_TIER_RAW}"
       shift 2
       ;;
     --in-place|--allow-in-place)
@@ -246,11 +246,45 @@ normalize_bool() {
 
 OPENSPEC_AUTO_INIT="$(normalize_bool "$OPENSPEC_AUTO_INIT_RAW" "1")"
 
+normalize_tier() {
+  local raw="${1:-}"
+  local fallback="${2:-T3}"
+  local upper
+  upper="$(printf '%s' "$raw" | tr '[:lower:]' '[:upper:]')"
+  case "$upper" in
+    T0|T1|T2|T3) printf '%s' "$upper" ;;
+    '') printf '%s' "$fallback" ;;
+    *) return 1 ;;
+  esac
+}
+
+if ! OPENSPEC_TIER="$(normalize_tier "$OPENSPEC_TIER_RAW" "T3")"; then
+  echo "[agent-branch-start] Unsupported OpenSpec tier: ${OPENSPEC_TIER_RAW}" >&2
+  exit 1
+fi
+
+OPENSPEC_SKIP_CHANGE=0
+OPENSPEC_SKIP_PLAN=0
+OPENSPEC_MINIMAL=0
+case "$OPENSPEC_TIER" in
+  T0)
+    OPENSPEC_SKIP_CHANGE=1
+    OPENSPEC_SKIP_PLAN=1
+    ;;
+  T1)
+    OPENSPEC_SKIP_PLAN=1
+    OPENSPEC_MINIMAL=1
+    ;;
+  T2)
+    OPENSPEC_SKIP_PLAN=1
+    ;;
+esac
+
 resolve_openspec_masterplan_label() {
   local raw="${OPENSPEC_MASTERPLAN_LABEL_RAW:-}"
   local label
 
-  if [[ "$OPENSPEC_AUTO_INIT" -ne 1 ]] || [[ -z "$raw" ]]; then
+  if [[ "$OPENSPEC_AUTO_INIT" -ne 1 ]] || [[ "$OPENSPEC_SKIP_PLAN" -eq 1 ]] || [[ -z "$raw" ]]; then
     printf ''
     return 0
   fi
@@ -404,7 +438,7 @@ initialize_openspec_plan_workspace() {
   local worktree="$2"
   local plan_slug="$3"
 
-  if [[ "$OPENSPEC_AUTO_INIT" -ne 1 ]]; then
+  if [[ "$OPENSPEC_AUTO_INIT" -ne 1 ]] || [[ "$OPENSPEC_SKIP_PLAN" -eq 1 ]]; then
     return 0
   fi
 
@@ -430,14 +464,15 @@ initialize_openspec_change_workspace() {
   local change_slug="$3"
   local capability_slug="$4"
 
-  if [[ "$OPENSPEC_AUTO_INIT" -ne 1 ]]; then
+  if [[ "$OPENSPEC_AUTO_INIT" -ne 1 ]] || [[ "$OPENSPEC_SKIP_CHANGE" -eq 1 ]]; then
     return 0
   fi
 
   local init_output=""
   if ! init_output="$(
     cd "$worktree"
-    run_guardex_cli internal run-shell changeInit "$change_slug" "$capability_slug" 2>&1
+    GUARDEX_OPENSPEC_MINIMAL="$OPENSPEC_MINIMAL" \
+      run_guardex_cli internal run-shell changeInit "$change_slug" "$capability_slug" 2>&1
   )"; then
     printf '%s\n' "$init_output" >&2
     echo "[agent-branch-start] OpenSpec workspace initialization failed for change '${change_slug}'." >&2
@@ -599,8 +634,17 @@ fi
 
 echo "[agent-branch-start] Created branch: ${branch_name}"
 echo "[agent-branch-start] Worktree: ${worktree_path}"
-echo "[agent-branch-start] OpenSpec change: openspec/changes/${openspec_change_slug}"
-echo "[agent-branch-start] OpenSpec plan: openspec/plan/${openspec_plan_slug}"
+echo "[agent-branch-start] OpenSpec tier: ${OPENSPEC_TIER}"
+if [[ "$OPENSPEC_SKIP_CHANGE" -eq 1 ]]; then
+  echo "[agent-branch-start] OpenSpec change: skipped by tier ${OPENSPEC_TIER}"
+else
+  echo "[agent-branch-start] OpenSpec change: openspec/changes/${openspec_change_slug}"
+fi
+if [[ "$OPENSPEC_SKIP_PLAN" -eq 1 ]]; then
+  echo "[agent-branch-start] OpenSpec plan: skipped by tier ${OPENSPEC_TIER}"
+else
+  echo "[agent-branch-start] OpenSpec plan: openspec/plan/${openspec_plan_slug}"
+fi
 echo "[agent-branch-start] Next steps:"
 echo "  cd \"${worktree_path}\""
 echo "  gx locks claim --branch \"${branch_name}\" <file...>"
diff --git a/scripts/agent-session-state.js b/scripts/agent-session-state.js
index ae65c18..2e65554 100755
--- a/scripts/agent-session-state.js
+++ b/scripts/agent-session-state.js
@@ -23,7 +23,7 @@ const sessionSchema = resolveSessionSchemaModule();
 function usage() {
   return (
     'Usage:\n' +
-    '  node scripts/agent-session-state.js start --repo <path> --branch <name> --task <task> --agent <agent> --worktree <path> --pid <pid> --cli <name>\n' +
+    '  node scripts/agent-session-state.js start --repo <path> --branch <name> --task <task> --agent <agent> --worktree <path> --pid <pid> --cli <name> [--task-mode <caveman|omx>] [--openspec-tier <T0|T1|T2|T3>] [--routing-reason <text>]\n' +
     '  node scripts/agent-session-state.js stop --repo <path> --branch <name>\n'
   );
 }
@@ -65,6 +65,9 @@ function writeSessionRecord(options) {
     worktreePath: requireOption(options, 'worktree'),
     pid: requireOption(options, 'pid'),
     cliName: requireOption(options, 'cli'),
+    taskMode: options['task-mode'],
+    openspecTier: options['openspec-tier'],
+    taskRoutingReason: options['routing-reason'],
   });
 
   const targetPath = sessionSchema.sessionFilePathForBranch(repoRoot, branch);
diff --git a/scripts/codex-agent.sh b/scripts/codex-agent.sh
index 6a05817..e287707 100755
--- a/scripts/codex-agent.sh
+++ b/scripts/codex-agent.sh
@@ -17,6 +17,13 @@ OPENSPEC_PLAN_SLUG_OVERRIDE="${GUARDEX_OPENSPEC_PLAN_SLUG:-}"
 OPENSPEC_CHANGE_SLUG_OVERRIDE="${GUARDEX_OPENSPEC_CHANGE_SLUG:-}"
 OPENSPEC_CAPABILITY_SLUG_OVERRIDE="${GUARDEX_OPENSPEC_CAPABILITY_SLUG:-}"
 OPENSPEC_MASTERPLAN_LABEL_RAW="${GUARDEX_OPENSPEC_MASTERPLAN_LABEL-masterplan}"
+OPENSPEC_TIER_RAW="${GUARDEX_OPENSPEC_TIER:-}"
+OPENSPEC_TIER=""
+OPENSPEC_SKIP_CHANGE=0
+OPENSPEC_SKIP_PLAN=0
+OPENSPEC_MINIMAL=0
+TASK_MODE=""
+TASK_ROUTING_REASON=""
 
 run_guardex_cli() {
   if [[ -n "$CLI_ENTRY" ]]; then
@@ -48,6 +55,117 @@ normalize_bool() {
   esac
 }
 
+normalize_tier() {
+  local raw="${1:-}"
+  local fallback="${2:-T2}"
+  local upper
+  upper="$(printf '%s' "$raw" | tr '[:lower:]' '[:upper:]')"
+  case "$upper" in
+    T0|T1|T2|T3) printf '%s' "$upper" ;;
+    '') printf '%s' "$fallback" ;;
+    *) return 1 ;;
+  esac
+}
+
+string_contains_any() {
+  local haystack="$1"
+  shift
+  local needle
+  for needle in "$@"; do
+    if [[ "$haystack" == *"$needle"* ]]; then
+      return 0
+    fi
+  done
+  return 1
+}
+
+string_has_lightweight_prefix() {
+  local text="$1"
+  local prefix
+  for prefix in "quick:" "simple:" "tiny:" "minor:" "small:" "just:" "only:"; do
+    if [[ "$text" == "$prefix"* ]]; then
+      return 0
+    fi
+  done
+  return 1
+}
+
+derive_task_mode_from_tier() {
+  case "$1" in
+    T0|T1) printf 'caveman' ;;
+    T2|T3) printf 'omx' ;;
+    *) return 1 ;;
+  esac
+}
+
+apply_openspec_tier() {
+  OPENSPEC_SKIP_CHANGE=0
+  OPENSPEC_SKIP_PLAN=0
+  OPENSPEC_MINIMAL=0
+  case "$1" in
+    T0)
+      OPENSPEC_SKIP_CHANGE=1
+      OPENSPEC_SKIP_PLAN=1
+      ;;
+    T1)
+      OPENSPEC_SKIP_PLAN=1
+      OPENSPEC_MINIMAL=1
+      ;;
+    T2)
+      OPENSPEC_SKIP_PLAN=1
+      ;;
+  esac
+}
+
+decide_task_routing() {
+  local task_lower
+  task_lower="$(printf '%s' "$TASK_NAME" | tr '[:upper:]' '[:lower:]')"
+
+  if [[ -n "$OPENSPEC_TIER_RAW" ]]; then
+    if ! OPENSPEC_TIER="$(normalize_tier "$OPENSPEC_TIER_RAW" "T2")"; then
+      echo "[codex-agent] Unsupported OpenSpec tier: ${OPENSPEC_TIER_RAW}" >&2
+      return 1
+    fi
+    TASK_ROUTING_REASON="explicit tier override"
+  elif string_has_lightweight_prefix "$task_lower"; then
+    OPENSPEC_TIER="T1"
+    TASK_ROUTING_REASON="explicit lightweight prefix"
+  elif string_contains_any "$task_lower" \
+    "ralph" "autopilot" "ultrawork" "ultraqa" "ralplan" "deep interview" "ouroboros" \
+    "migration" "refactor" "architecture" "re-architect" "cross-cutting" "multi-agent" \
+    "multiagent" "parallel" "orchestr" "release" "zero-copy" "install surface" "workflow"
+  then
+    OPENSPEC_TIER="T3"
+    TASK_ROUTING_REASON="plan-heavy or orchestration-heavy task wording"
+  elif string_contains_any "$task_lower" \
+    "typo" "spelling" "comment-only" "comment only" "format-only" "format only" \
+    "whitespace" "one-liner" "one liner" "version bump" "bump version" \
+    "single-file" "single file"
+  then
+    OPENSPEC_TIER="T1"
+    TASK_ROUTING_REASON="small bounded maintenance wording"
+  else
+    OPENSPEC_TIER="T2"
+    TASK_ROUTING_REASON="default behavior-change route"
+  fi
+
+  if ! TASK_MODE="$(derive_task_mode_from_tier "$OPENSPEC_TIER")"; then
+    echo "[codex-agent] Unsupported task mode tier: ${OPENSPEC_TIER}" >&2
+    return 1
+  fi
+  apply_openspec_tier "$OPENSPEC_TIER"
+}
+
+describe_task_routing() {
+  case "$OPENSPEC_TIER" in
+    T0) printf 'caveman / T0 (no OpenSpec scaffold)' ;;
+    T1) printf 'caveman / T1 (notes-only OpenSpec)' ;;
+    T2) printf 'omx / T2 (change workspace only)' ;;
+    T3) printf 'omx / T3 (change plus plan workspace)' ;;
+    *) printf 'unknown / %s' "${OPENSPEC_TIER:-unset}" ;;
+  esac
+}
+
 AUTO_FINISH="$(normalize_bool "$AUTO_FINISH_RAW" "1")"
 AUTO_REVIEW_ON_CONFLICT="$(normalize_bool "$AUTO_REVIEW_ON_CONFLICT_RAW" "1")"
 AUTO_CLEANUP="$(normalize_bool "$AUTO_CLEANUP_RAW" "1")"
@@ -58,7 +176,7 @@ resolve_openspec_masterplan_label() {
   local raw="${OPENSPEC_MASTERPLAN_LABEL_RAW:-}"
   local label
 
-  if [[ "$OPENSPEC_AUTO_INIT" -ne 1 ]] || [[ -z "$raw" ]]; then
+  if [[ "$OPENSPEC_AUTO_INIT" -ne 1 ]] || [[ "$OPENSPEC_SKIP_PLAN" -eq 1 ]] || [[ -z "$raw" ]]; then
     printf ''
     return 0
   fi
@@ -86,6 +204,10 @@ while [[ $# -gt 0 ]]; do
       BASE_BRANCH_EXPLICIT=1
       shift 2
       ;;
+    --tier)
+      OPENSPEC_TIER_RAW="${2:-$OPENSPEC_TIER_RAW}"
+      shift 2
+      ;;
     --codex-bin)
       CODEX_BIN="${2:-$CODEX_BIN}"
       shift 2
@@ -151,6 +273,10 @@ if [[ "$BASE_BRANCH_EXPLICIT" -eq 1 && -z "$BASE_BRANCH" ]]; then
   exit 1
 fi
 
+if ! decide_task_routing; then
+  exit 1
+fi
+
 if ! command -v "$CODEX_BIN" >/dev/null 2>&1; then
   echo "[codex-agent] Missing Codex CLI command: $CODEX_BIN" >&2
   echo "[codex-agent] Install Codex first, then retry." >&2
@@ -393,7 +519,7 @@ start_sandbox_fallback() {
   printf '[agent-branch-start] Worktree: %s\n' "$worktree_path"
 }
 
-start_args=("$TASK_NAME" "$AGENT_NAME")
+start_args=(--tier "$OPENSPEC_TIER" "$TASK_NAME" "$AGENT_NAME")
 if [[ "$BASE_BRANCH_EXPLICIT" -eq 1 ]]; then
   start_args+=("$BASE_BRANCH")
 fi
@@ -487,7 +613,10 @@ record_active_session_state() {
     --agent "$AGENT_NAME" \
     --worktree "$wt" \
     --pid "$$" \
-    --cli "$CODEX_BIN"
+    --cli "$CODEX_BIN" \
+    --task-mode "$TASK_MODE" \
+    --openspec-tier "$OPENSPEC_TIER" \
+    --routing-reason "$TASK_ROUTING_REASON"
 }
 
 clear_active_session_state() {
@@ -545,6 +674,7 @@ print_takeover_prompt() {
   finish_cmd="gx branch finish --branch \"${branch}\" --base ${base_branch} --via-pr --wait-for-merge --cleanup"
 
   echo "[codex-agent] Takeover sandbox: ${wt}"
+  echo "[codex-agent] Takeover routing: $(describe_task_routing) (${TASK_ROUTING_REASON})"
   echo "[codex-agent] Takeover prompt: Continue \`${change_slug}\` on branch \`${branch}\`. Work inside \`${wt}\`, review \`${change_artifact}\`, continue from the current state instead of creating a new sandbox, and when the work is done run \`${finish_cmd}\`."
 }
 
@@ -594,7 +724,7 @@ ensure_openspec_plan_workspace() {
   local wt="$1"
   local branch="$2"
 
-  if [[ "$OPENSPEC_AUTO_INIT" -ne 1 ]]; then
+  if [[ "$OPENSPEC_AUTO_INIT" -ne 1 ]] || [[ "$OPENSPEC_SKIP_PLAN" -eq 1 ]]; then
     return 0
   fi
 
@@ -619,7 +749,7 @@ ensure_openspec_change_workspace() {
   local wt="$1"
   local branch="$2"
 
-  if [[ "$OPENSPEC_AUTO_INIT" -ne 1 ]]; then
+  if [[ "$OPENSPEC_AUTO_INIT" -ne 1 ]] || [[ "$OPENSPEC_SKIP_CHANGE" -eq 1 ]]; then
     return 0
   fi
 
@@ -628,7 +758,8 @@ ensure_openspec_change_workspace() {
   capability_slug="$(resolve_openspec_capability_slug)"
   if ! init_output="$(
     cd "$wt"
-    run_guardex_cli internal run-shell changeInit "$change_slug" "$capability_slug" 2>&1
+    GUARDEX_OPENSPEC_MINIMAL="$OPENSPEC_MINIMAL" \
+      run_guardex_cli internal run-shell changeInit "$change_slug" "$capability_slug" 2>&1
   )"; then
     printf '%s\n' "$init_output" >&2
     echo "[codex-agent] OpenSpec workspace initialization failed for change '${change_slug}'." >&2
@@ -878,6 +1009,8 @@ if ! ensure_openspec_plan_workspace "$worktree_path" "$worktree_branch"; then
   exit 1
 fi
 
+echo "[codex-agent] Task routing: $(describe_task_routing) (${TASK_ROUTING_REASON})"
+
 active_session_recorded=0
 cleanup_active_session_state_on_exit() {
   set +e
@@ -894,7 +1027,10 @@ trap cleanup_active_session_state_on_exit EXIT INT TERM
 echo "[codex-agent] Launching ${CODEX_BIN} in sandbox: $worktree_path"
 cd "$worktree_path"
 set +e
-"$CODEX_BIN" "$@"
+GUARDEX_TASK_MODE="$TASK_MODE" \
+GUARDEX_OPENSPEC_TIER="$OPENSPEC_TIER" \
+GUARDEX_TASK_ROUTING_REASON="$TASK_ROUTING_REASON" \
+  "$CODEX_BIN" "$@"
 codex_exit="$?"
 set -e
 
diff --git a/templates/scripts/agent-branch-start.sh b/templates/scripts/agent-branch-start.sh
index c871372..9da6d60 100755
--- a/templates/scripts/agent-branch-start.sh
+++ b/templates/scripts/agent-branch-start.sh
@@ -14,6 +14,7 @@ OPENSPEC_PLAN_SLUG_OVERRIDE="${GUARDEX_OPENSPEC_PLAN_SLUG:-}"
 OPENSPEC_CHANGE_SLUG_OVERRIDE="${GUARDEX_OPENSPEC_CHANGE_SLUG:-}"
 OPENSPEC_CAPABILITY_SLUG_OVERRIDE="${GUARDEX_OPENSPEC_CAPABILITY_SLUG:-}"
 OPENSPEC_MASTERPLAN_LABEL_RAW="${GUARDEX_OPENSPEC_MASTERPLAN_LABEL-masterplan}"
+OPENSPEC_TIER_RAW="${GUARDEX_OPENSPEC_TIER:-T3}"
 PRINT_NAME_ONLY=0
 POSITIONAL_ARGS=()
 
@@ -54,8 +55,7 @@ while [[ $# -gt 0 ]]; do
       shift
       ;;
     --tier)
-      # Accepted for CLAUDE.md compatibility; scaffold size is not yet wired
-      # through this script. Consume the value so callers can pass it.
+      OPENSPEC_TIER_RAW="${2:-$OPENSPEC_TIER_RAW}"
       shift 2
       ;;
     --in-place|--allow-in-place)
@@ -246,11 +246,45 @@ normalize_bool() {
 
 OPENSPEC_AUTO_INIT="$(normalize_bool "$OPENSPEC_AUTO_INIT_RAW" "1")"
 
+normalize_tier() {
+  local raw="${1:-}"
+  local fallback="${2:-T3}"
+  local upper
+  upper="$(printf '%s' "$raw" | tr '[:lower:]' '[:upper:]')"
+  case "$upper" in
+    T0|T1|T2|T3) printf '%s' "$upper" ;;
+    '') printf '%s' "$fallback" ;;
+    *) return 1 ;;
+  esac
+}
+
+if ! OPENSPEC_TIER="$(normalize_tier "$OPENSPEC_TIER_RAW" "T3")"; then
+  echo "[agent-branch-start] Unsupported OpenSpec tier: ${OPENSPEC_TIER_RAW}" >&2
+  exit 1
+fi
+
+OPENSPEC_SKIP_CHANGE=0
+OPENSPEC_SKIP_PLAN=0
+OPENSPEC_MINIMAL=0
+case "$OPENSPEC_TIER" in
+  T0)
+    OPENSPEC_SKIP_CHANGE=1
+    OPENSPEC_SKIP_PLAN=1
+    ;;
+  T1)
+    OPENSPEC_SKIP_PLAN=1
+    OPENSPEC_MINIMAL=1
+    ;;
+  T2)
+    OPENSPEC_SKIP_PLAN=1
+    ;;
+esac
+
 resolve_openspec_masterplan_label() {
   local raw="${OPENSPEC_MASTERPLAN_LABEL_RAW:-}"
   local label
 
-  if [[ "$OPENSPEC_AUTO_INIT" -ne 1 ]] || [[ -z "$raw" ]]; then
+  if [[ "$OPENSPEC_AUTO_INIT" -ne 1 ]] || [[ "$OPENSPEC_SKIP_PLAN" -eq 1 ]] || [[ -z "$raw" ]]; then
     printf ''
     return 0
   fi
@@ -404,7 +438,7 @@ initialize_openspec_plan_workspace() {
   local worktree="$2"
   local plan_slug="$3"
 
-  if [[ "$OPENSPEC_AUTO_INIT" -ne 1 ]]; then
+  if [[ "$OPENSPEC_AUTO_INIT" -ne 1 ]] || [[ "$OPENSPEC_SKIP_PLAN" -eq 1 ]]; then
     return 0
   fi
 
@@ -430,14 +464,15 @@ initialize_openspec_change_workspace() {
   local change_slug="$3"
   local capability_slug="$4"
 
-  if [[ "$OPENSPEC_AUTO_INIT" -ne 1 ]]; then
+  if [[ "$OPENSPEC_AUTO_INIT" -ne 1 ]] || [[ "$OPENSPEC_SKIP_CHANGE" -eq 1 ]]; then
     return 0
   fi
 
   local init_output=""
   if ! init_output="$(
     cd "$worktree"
-    run_guardex_cli internal run-shell changeInit "$change_slug" "$capability_slug" 2>&1
+    GUARDEX_OPENSPEC_MINIMAL="$OPENSPEC_MINIMAL" \
+      run_guardex_cli internal run-shell changeInit "$change_slug" "$capability_slug" 2>&1
   )"; then
     printf '%s\n' "$init_output" >&2
     echo "[agent-branch-start] OpenSpec workspace initialization failed for change '${change_slug}'." >&2
@@ -599,8 +634,17 @@ fi
 
 echo "[agent-branch-start] Created branch: ${branch_name}"
 echo "[agent-branch-start] Worktree: ${worktree_path}"
-echo "[agent-branch-start] OpenSpec change: openspec/changes/${openspec_change_slug}"
-echo "[agent-branch-start] OpenSpec plan: openspec/plan/${openspec_plan_slug}"
+echo "[agent-branch-start] OpenSpec tier: ${OPENSPEC_TIER}"
+if [[ "$OPENSPEC_SKIP_CHANGE" -eq 1 ]]; then
+  echo "[agent-branch-start] OpenSpec change: skipped by tier ${OPENSPEC_TIER}"
+else
+  echo "[agent-branch-start] OpenSpec change: openspec/changes/${openspec_change_slug}"
+fi
+if [[ "$OPENSPEC_SKIP_PLAN" -eq 1 ]]; then
+  echo "[agent-branch-start] OpenSpec plan: skipped by tier ${OPENSPEC_TIER}"
+else
+  echo "[agent-branch-start] OpenSpec plan: openspec/plan/${openspec_plan_slug}"
+fi
 echo "[agent-branch-start] Next steps:"
 echo "  cd \"${worktree_path}\""
 echo "  gx locks claim --branch \"${branch_name}\" <file...>"
diff --git a/templates/scripts/codex-agent.sh b/templates/scripts/codex-agent.sh
index 6a05817..e287707 100755
--- a/templates/scripts/codex-agent.sh
+++ b/templates/scripts/codex-agent.sh
@@ -17,6 +17,13 @@ OPENSPEC_PLAN_SLUG_OVERRIDE="${GUARDEX_OPENSPEC_PLAN_SLUG:-}"
 OPENSPEC_CHANGE_SLUG_OVERRIDE="${GUARDEX_OPENSPEC_CHANGE_SLUG:-}"
 OPENSPEC_CAPABILITY_SLUG_OVERRIDE="${GUARDEX_OPENSPEC_CAPABILITY_SLUG:-}"
 OPENSPEC_MASTERPLAN_LABEL_RAW="${GUARDEX_OPENSPEC_MASTERPLAN_LABEL-masterplan}"
+OPENSPEC_TIER_RAW="${GUARDEX_OPENSPEC_TIER:-}"
+OPENSPEC_TIER=""
+OPENSPEC_SKIP_CHANGE=0
+OPENSPEC_SKIP_PLAN=0
+OPENSPEC_MINIMAL=0
+TASK_MODE=""
+TASK_ROUTING_REASON=""
 
 run_guardex_cli() {
   if [[ -n "$CLI_ENTRY" ]]; then
@@ -48,6 +55,117 @@ normalize_bool() {
   esac
 }
 
+normalize_tier() {
+  local raw="${1:-}"
+  local fallback="${2:-T2}"
+  local upper
+  upper="$(printf '%s' "$raw" | tr '[:lower:]' '[:upper:]')"
+  case "$upper" in
+    T0|T1|T2|T3) printf '%s' "$upper" ;;
+    '') printf '%s' "$fallback" ;;
+    *) return 1 ;;
+  esac
+}
+
+string_contains_any() {
+  local haystack="$1"
+  shift
+  local needle
+  for needle in "$@"; do
+    if [[ "$haystack" == *"$needle"* ]]; then
+      return 0
+    fi
+  done
+  return 1
+}
+
+string_has_lightweight_prefix() {
+  local text="$1"
+  local prefix
+  for prefix in "quick:" "simple:" "tiny:" "minor:" "small:" "just:" "only:"; do
+    if [[ "$text" == "$prefix"* ]]; then
+      return 0
+    fi
+  done
+  return 1
+}
+
+derive_task_mode_from_tier() {
+  case "$1" in
+    T0|T1) printf 'caveman' ;;
+    T2|T3) printf 'omx' ;;
+    *) return 1 ;;
+  esac
+}
+
+apply_openspec_tier() {
+  OPENSPEC_SKIP_CHANGE=0
+  OPENSPEC_SKIP_PLAN=0
+  OPENSPEC_MINIMAL=0
+  case "$1" in
+    T0)
+      OPENSPEC_SKIP_CHANGE=1
+      OPENSPEC_SKIP_PLAN=1
+      ;;
+    T1)
+      OPENSPEC_SKIP_PLAN=1
+      OPENSPEC_MINIMAL=1
+      ;;
+    T2)
+      OPENSPEC_SKIP_PLAN=1
+      ;;
+  esac
+}
+
+decide_task_routing() {
+  local task_lower
+  task_lower="$(printf '%s' "$TASK_NAME" | tr '[:upper:]' '[:lower:]')"
+
+  if [[ -n "$OPENSPEC_TIER_RAW" ]]; then
+    if ! OPENSPEC_TIER="$(normalize_tier "$OPENSPEC_TIER_RAW" "T2")"; then
+      echo "[codex-agent] Unsupported OpenSpec tier: ${OPENSPEC_TIER_RAW}" >&2
+      return 1
+    fi
+    TASK_ROUTING_REASON="explicit tier override"
+  elif string_has_lightweight_prefix "$task_lower"; then
+    OPENSPEC_TIER="T1"
+    TASK_ROUTING_REASON="explicit lightweight prefix"
+  elif string_contains_any "$task_lower" \
+    "ralph" "autopilot" "ultrawork" "ultraqa" "ralplan" "deep interview" "ouroboros" \
+    "migration" "refactor" "architecture" "re-architect" "cross-cutting" "multi-agent" \
+    "multiagent" "parallel" "orchestr" "release" "zero-copy" "install surface" "workflow"
+  then
+    OPENSPEC_TIER="T3"
+    TASK_ROUTING_REASON="plan-heavy or orchestration-heavy task wording"
+  elif string_contains_any "$task_lower" \
+    "typo" "spelling" "comment-only" "comment only" "format-only" "format only" \
+    "whitespace" "one-liner" "one liner" "version bump" "bump version" \
+    "single-file" "single file"
+  then
+    OPENSPEC_TIER="T1"
+    TASK_ROUTING_REASON="small bounded maintenance wording"
+  else
+    OPENSPEC_TIER="T2"
+    TASK_ROUTING_REASON="default behavior-change route"
+  fi
+
+  if ! TASK_MODE="$(derive_task_mode_from_tier "$OPENSPEC_TIER")"; then
+    echo "[codex-agent] Unsupported task mode tier: ${OPENSPEC_TIER}" >&2
+    return 1
+  fi
+  apply_openspec_tier "$OPENSPEC_TIER"
+}
+
+describe_task_routing() {
+  case "$OPENSPEC_TIER" in
+    T0) printf 'caveman / T0 (no OpenSpec scaffold)' ;;
+    T1) printf 'caveman / T1 (notes-only OpenSpec)' ;;
+    T2) printf 'omx / T2 (change workspace only)' ;;
+    T3) printf 'omx / T3 (change plus plan workspace)' ;;
+    *) printf 'unknown / %s' "${OPENSPEC_TIER:-unset}" ;;
+  esac
+}
+
 AUTO_FINISH="$(normalize_bool "$AUTO_FINISH_RAW" "1")"
 AUTO_REVIEW_ON_CONFLICT="$(normalize_bool "$AUTO_REVIEW_ON_CONFLICT_RAW" "1")"
 AUTO_CLEANUP="$(normalize_bool "$AUTO_CLEANUP_RAW" "1")"
@@ -58,7 +176,7 @@ resolve_openspec_masterplan_label() {
   local raw="${OPENSPEC_MASTERPLAN_LABEL_RAW:-}"
   local label
 
-  if [[ "$OPENSPEC_AUTO_INIT" -ne 1 ]] || [[ -z "$raw" ]]; then
+  if [[ "$OPENSPEC_AUTO_INIT" -ne 1 ]] || [[ "$OPENSPEC_SKIP_PLAN" -eq 1 ]] || [[ -z "$raw" ]]; then
     printf ''
     return 0
   fi
@@ -86,6 +204,10 @@ while [[ $# -gt 0 ]]; do
       BASE_BRANCH_EXPLICIT=1
       shift 2
       ;;
+    --tier)
+      OPENSPEC_TIER_RAW="${2:-$OPENSPEC_TIER_RAW}"
+      shift 2
+      ;;
     --codex-bin)
       CODEX_BIN="${2:-$CODEX_BIN}"
       shift 2
@@ -151,6 +273,10 @@ if [[ "$BASE_BRANCH_EXPLICIT" -eq 1 && -z "$BASE_BRANCH" ]]; then
   exit 1
 fi
 
+if ! decide_task_routing; then
+  exit 1
+fi
+
 if ! command -v "$CODEX_BIN" >/dev/null 2>&1; then
   echo "[codex-agent] Missing Codex CLI command: $CODEX_BIN" >&2
   echo "[codex-agent] Install Codex first, then retry." >&2
@@ -393,7 +519,7 @@ start_sandbox_fallback() {
   printf '[agent-branch-start] Worktree: %s\n' "$worktree_path"
 }
 
-start_args=("$TASK_NAME" "$AGENT_NAME")
+start_args=(--tier "$OPENSPEC_TIER" "$TASK_NAME" "$AGENT_NAME")
 if [[ "$BASE_BRANCH_EXPLICIT" -eq 1 ]]; then
   start_args+=("$BASE_BRANCH")
 fi
@@ -487,7 +613,10 @@ record_active_session_state() {
     --agent "$AGENT_NAME" \
     --worktree "$wt" \
     --pid "$$" \
-    --cli "$CODEX_BIN"
+    --cli "$CODEX_BIN" \
+    --task-mode "$TASK_MODE" \
+    --openspec-tier "$OPENSPEC_TIER" \
+    --routing-reason "$TASK_ROUTING_REASON"
 }
 
 clear_active_session_state() {
@@ -545,6 +674,7 @@ print_takeover_prompt() {
   finish_cmd="gx branch finish --branch \"${branch}\" --base ${base_branch} --via-pr --wait-for-merge --cleanup"
 
   echo "[codex-agent] Takeover sandbox: ${wt}"
+  echo "[codex-agent] Takeover routing: $(describe_task_routing) (${TASK_ROUTING_REASON})"
   echo "[codex-agent] Takeover prompt: Continue \`${change_slug}\` on branch \`${branch}\`. Work inside \`${wt}\`, review \`${change_artifact}\`, continue from the current state instead of creating a new sandbox, and when the work is done run \`${finish_cmd}\`."
 }
 
@@ -594,7 +724,7 @@ ensure_openspec_plan_workspace() {
   local wt="$1"
   local branch="$2"
 
-  if [[ "$OPENSPEC_AUTO_INIT" -ne 1 ]]; then
+  if [[ "$OPENSPEC_AUTO_INIT" -ne 1 ]] || [[ "$OPENSPEC_SKIP_PLAN" -eq 1 ]]; then
     return 0
   fi
 
@@ -619,7 +749,7 @@ ensure_openspec_change_workspace() {
   local wt="$1"
   local branch="$2"
 
-  if [[ "$OPENSPEC_AUTO_INIT" -ne 1 ]]; then
+  if [[ "$OPENSPEC_AUTO_INIT" -ne 1 ]] || [[ "$OPENSPEC_SKIP_CHANGE" -eq 1 ]]; then
     return 0
   fi
 
@@ -628,7 +758,8 @@ ensure_openspec_change_workspace() {
   capability_slug="$(resolve_openspec_capability_slug)"
   if ! init_output="$(
     cd "$wt"
-    run_guardex_cli internal run-shell changeInit "$change_slug" "$capability_slug" 2>&1
+    GUARDEX_OPENSPEC_MINIMAL="$OPENSPEC_MINIMAL" \
+      run_guardex_cli internal run-shell changeInit "$change_slug" "$capability_slug" 2>&1
   )"; then
     printf '%s\n' "$init_output" >&2
     echo "[codex-agent] OpenSpec workspace initialization failed for change '${change_slug}'." >&2
@@ -878,6 +1009,8 @@ if ! ensure_openspec_plan_workspace "$worktree_path" "$worktree_branch"; then
   exit 1
 fi
 
+echo "[codex-agent] Task routing: $(describe_task_routing) (${TASK_ROUTING_REASON})"
+
 active_session_recorded=0
 cleanup_active_session_state_on_exit() {
   set +e
@@ -894,7 +1027,10 @@ trap cleanup_active_session_state_on_exit EXIT INT TERM
 echo "[codex-agent] Launching ${CODEX_BIN} in sandbox: $worktree_path"
 cd "$worktree_path"
 set +e
-"$CODEX_BIN" "$@"
+GUARDEX_TASK_MODE="$TASK_MODE" \
+GUARDEX_OPENSPEC_TIER="$OPENSPEC_TIER" \
+GUARDEX_TASK_ROUTING_REASON="$TASK_ROUTING_REASON" \
+  "$CODEX_BIN" "$@"
 codex_exit="$?"
 set -e
 
diff --git a/templates/vscode/guardex-active-agents/session-schema.js b/templates/vscode/guardex-active-agents/session-schema.js
index e9282a0..fd4feca 100644
--- a/templates/vscode/guardex-active-agents/session-schema.js
+++ b/templates/vscode/guardex-active-agents/session-schema.js
@@ -35,6 +35,16 @@ function toPositiveInteger(value) {
   return Number.isInteger(normalized) && normalized > 0 ? normalized : null;
 }
 
+function normalizeTaskMode(value) {
+  const normalized = toNonEmptyString(value).toLowerCase();
+  return normalized === 'caveman' || normalized === 'omx' ? normalized : '';
+}
+
+function normalizeOpenSpecTier(value) {
+  const normalized = toNonEmptyString(value).toUpperCase();
+  return ['T0', 'T1', 'T2', 'T3'].includes(normalized) ? normalized : '';
+}
+
 function sanitizeBranchForFile(branch) {
   const normalized = toNonEmptyString(branch, 'session');
   return normalized.replace(/[^a-zA-Z0-9._-]+/g, '__').replace(/^_+|_+$/g, '') || 'session';
@@ -420,6 +430,9 @@ function buildSessionRecord(input) {
     worktreePath,
     pid,
     cliName: toNonEmptyString(input.cliName, 'codex'),
+    taskMode: normalizeTaskMode(input.taskMode),
+    openspecTier: normalizeOpenSpecTier(input.openspecTier),
+    taskRoutingReason: toNonEmptyString(input.taskRoutingReason),
     startedAt: startedAt.toISOString(),
   };
 }
@@ -456,6 +469,9 @@ function normalizeSessionRecord(input, options = {}) {
     worktreePath: path.resolve(worktreePath),
     pid,
     cliName: toNonEmptyString(input.cliName, 'codex'),
+    taskMode: normalizeTaskMode(input.taskMode),
+    openspecTier: normalizeOpenSpecTier(input.openspecTier),
+    taskRoutingReason: toNonEmptyString(input.taskRoutingReason),
     startedAt: startedAt.toISOString(),
     filePath: toNonEmptyString(options.filePath),
     label: deriveSessionLabel(branch, worktreePath),
diff --git a/test/branch.test.js b/test/branch.test.js
index a0d9280..08ad465 100644
--- a/test/branch.test.js
+++ b/test/branch.test.js
@@ -233,6 +233,86 @@ test('agent-branch-start links dependency node_modules directories into new work
 });
 
 
+test('agent-branch-start honors T1 notes-only OpenSpec scaffolding', () => {
+  const repoDir = initRepo();
+  seedCommit(repoDir);
+
+  let result = runNode(['setup', '--target', repoDir, '--no-global-install'], repoDir);
+  assert.equal(result.status, 0, result.stderr || result.stdout);
+
+  result = runCmd('git', ['add', '.'], repoDir);
+  assert.equal(result.status, 0, result.stderr || result.stdout);
+  result = runCmd('git', ['commit', '-m', 'apply gx setup'], repoDir, {
+    ALLOW_COMMIT_ON_PROTECTED_BRANCH: '1',
+  });
+  assert.equal(result.status, 0, result.stderr || result.stdout);
+
+  result = runBranchStart(['--tier', 'T1', 'simple: tighten copy', 'bot'], repoDir, {
+    GUARDEX_OPENSPEC_AUTO_INIT: 'true',
+  });
+  assert.equal(result.status, 0, result.stderr || result.stdout);
+  assert.match(result.stdout, /\[agent-branch-start\] OpenSpec tier: T1/);
+  assert.match(result.stdout, /\[agent-branch-start\] OpenSpec plan: skipped by tier T1/);
+
+  const createdWorktree = extractCreatedWorktree(result.stdout);
+  const changeSlug = extractOpenSpecChangeSlug(result.stdout);
+  const changeDir = path.join(createdWorktree, 'openspec', 'changes', changeSlug);
+
+  assert.doesNotMatch(createdWorktree, /masterplan/);
+  assert.equal(fs.existsSync(path.join(changeDir, '.openspec.yaml')), true, '.openspec.yaml missing');
+  assert.equal(fs.existsSync(path.join(changeDir, 'notes.md')), true, 'notes.md missing');
+  assert.equal(fs.existsSync(path.join(changeDir, 'proposal.md')), false, 'proposal.md should be absent for T1');
+  assert.equal(fs.existsSync(path.join(changeDir, 'tasks.md')), false, 'tasks.md should be absent for T1');
+  assert.equal(
+    fs.existsSync(path.join(createdWorktree, 'openspec', 'plan', changeSlug)),
+    false,
+    'T1 branch start should not create a plan workspace',
+  );
+});
+
+
+test('agent-branch-start honors T2 full change scaffolding without a plan workspace', () => {
+  const repoDir = initRepo();
+  seedCommit(repoDir);
+
+  let result = runNode(['setup', '--target', repoDir, '--no-global-install'], repoDir);
+  assert.equal(result.status, 0, result.stderr || result.stdout);
+
+  result = runCmd('git', ['add', '.'], repoDir);
+  assert.equal(result.status, 0, result.stderr || result.stdout);
+  result = runCmd('git', ['commit', '-m', 'apply gx setup'], repoDir, {
+    ALLOW_COMMIT_ON_PROTECTED_BRANCH: '1',
+  });
+  assert.equal(result.status, 0, result.stderr || result.stdout);
+
+  result = runBranchStart(['--tier', 'T2', 'improve-routing-decider', 'bot'], repoDir, {
+    GUARDEX_OPENSPEC_AUTO_INIT: 'true',
+  });
+  assert.equal(result.status, 0, result.stderr || result.stdout);
+  assert.match(result.stdout, /\[agent-branch-start\] OpenSpec tier: T2/);
+  assert.match(result.stdout, /\[agent-branch-start\] OpenSpec plan: skipped by tier T2/);
+
+  const createdWorktree = extractCreatedWorktree(result.stdout);
+  const changeSlug = extractOpenSpecChangeSlug(result.stdout);
+  const changeDir = path.join(createdWorktree, 'openspec', 'changes', changeSlug);
+
+  assert.doesNotMatch(createdWorktree, /masterplan/);
+  assert.equal(fs.existsSync(path.join(changeDir, '.openspec.yaml')), true, '.openspec.yaml missing');
+  assert.equal(fs.existsSync(path.join(changeDir, 'proposal.md')), true, 'proposal.md missing');
+  assert.equal(fs.existsSync(path.join(changeDir, 'tasks.md')), true, 'tasks.md missing');
+  assert.equal(
+    fs.existsSync(path.join(changeDir, 'specs', 'improve-routing-decider', 'spec.md')),
+    true,
+    'spec.md missing',
+  );
+  assert.equal(
+    fs.existsSync(path.join(createdWorktree, 'openspec', 'plan', changeSlug)),
+    false,
+    'T2 branch start should not create a plan workspace',
+  );
+});
+
+
 test('protect command manages configured protected branches', () => {
   const repoDir = initRepo();
   seedCommit(repoDir);
diff --git a/test/sandbox.test.js b/test/sandbox.test.js
index f031369..b85bc13 100644
--- a/test/sandbox.test.js
+++ b/test/sandbox.test.js
@@ -89,7 +89,7 @@ test('codex-agent launches codex inside a fresh sandbox worktree and keeps branc
 
   const cwdMarker = path.join(repoDir, '.codex-agent-cwd');
   const argsMarker = path.join(repoDir, '.codex-agent-args');
-  const launch = runCodexAgent(['launch-task', 'planner', 'dev', '--model', 'gpt-5.4-mini'], repoDir, {
+  const launch = runCodexAgent(['--tier', 'T3', 'launch-task', 'planner', 'dev', '--model', 'gpt-5.4-mini'], repoDir, {
     PATH: `${fakeBin}:${process.env.PATH}`,
     GUARDEX_TEST_CODEX_CWD: cwdMarker,
     GUARDEX_TEST_CODEX_ARGS: argsMarker,
@@ -141,6 +141,73 @@ test('codex-agent launches codex inside a fresh sandbox worktree and keeps branc
 });
 
 
+test('codex-agent routes lightweight tasks to caveman T1 with notes-only OpenSpec', () => {
+  const repoDir = initRepo();
+  seedCommit(repoDir);
+
+  const setupResult = runNode(['setup', '--target', repoDir, '--no-global-install'], repoDir);
+  assert.equal(setupResult.status, 0, setupResult.stderr || setupResult.stdout);
+  let result = runCmd('git', ['add', '.'], repoDir);
+  assert.equal(result.status, 0, result.stderr);
+  result = runCmd('git', ['commit', '-m', 'apply gx setup'], repoDir, {
+    ALLOW_COMMIT_ON_PROTECTED_BRANCH: '1',
+  });
+  assert.equal(result.status, 0, result.stderr || result.stdout);
+
+  const fakeBin = fs.mkdtempSync(path.join(os.tmpdir(), 'guardex-fake-codex-lightweight-'));
+  const fakeCodexPath = path.join(fakeBin, 'codex');
+  fs.writeFileSync(
+    fakeCodexPath,
+    `#!/usr/bin/env bash\n` +
+      `pwd > "${'${GUARDEX_TEST_CODEX_CWD}'}"\n` +
+      `echo "$@" > "${'${GUARDEX_TEST_CODEX_ARGS}'}"\n` +
+      `printf '%s' "${'${GUARDEX_TASK_MODE}'}" > "${'${GUARDEX_TEST_TASK_MODE}'}"\n` +
+      `printf '%s' "${'${GUARDEX_OPENSPEC_TIER}'}" > "${'${GUARDEX_TEST_TASK_TIER}'}"\n` +
+      `printf '%s' "${'${GUARDEX_TASK_ROUTING_REASON}'}" > "${'${GUARDEX_TEST_TASK_REASON}'}"\n`,
+    'utf8',
+  );
+  fs.chmodSync(fakeCodexPath, 0o755);
+
+  const cwdMarker = path.join(repoDir, '.codex-agent-cwd-lightweight');
+  const argsMarker = path.join(repoDir, '.codex-agent-args-lightweight');
+  const modeMarker = path.join(repoDir, '.codex-agent-mode-lightweight');
+  const tierMarker = path.join(repoDir, '.codex-agent-tier-lightweight');
+  const reasonMarker = path.join(repoDir, '.codex-agent-reason-lightweight');
+  const launch = runCodexAgent(['simple: tighten copy', 'planner', 'dev', '--model', 'gpt-5.4-mini'], repoDir, {
+    PATH: `${fakeBin}:${process.env.PATH}`,
+    GUARDEX_TEST_CODEX_CWD: cwdMarker,
+    GUARDEX_TEST_CODEX_ARGS: argsMarker,
+    GUARDEX_TEST_TASK_MODE: modeMarker,
+    GUARDEX_TEST_TASK_TIER: tierMarker,
+    GUARDEX_TEST_TASK_REASON: reasonMarker,
+  });
+  assert.equal(launch.status, 0, launch.stderr || launch.stdout);
+  assert.match(launch.stdout, /\[codex-agent\] Task routing: caveman \/ T1 \(notes-only OpenSpec\) \(explicit lightweight prefix\)/);
+  assert.doesNotMatch(launch.stdout, /\[codex-agent\] OpenSpec plan workspace:/);
+
+  const launchedCwd = fs.readFileSync(cwdMarker, 'utf8').trim();
+  const launchedBranch = extractCreatedBranch(launch.stdout);
+  const changeSlug = sanitizeSlug(launchedBranch, 'simple-tighten-copy');
+  const changeDir = path.join(launchedCwd, 'openspec', 'changes', changeSlug);
+  const launchedArgs = fs.readFileSync(argsMarker, 'utf8').trim();
+
+  assert.doesNotMatch(launchedCwd, /masterplan/);
+  assert.match(launchedArgs, /--model gpt-5\.4-mini/);
+  assert.equal(fs.readFileSync(modeMarker, 'utf8'), 'caveman');
+  assert.equal(fs.readFileSync(tierMarker, 'utf8'), 'T1');
+  assert.match(fs.readFileSync(reasonMarker, 'utf8'), /explicit lightweight prefix/);
+  assert.equal(fs.existsSync(path.join(changeDir, '.openspec.yaml')), true, '.openspec.yaml missing');
+  assert.equal(fs.existsSync(path.join(changeDir, 'notes.md')), true, 'notes.md missing');
+  assert.equal(fs.existsSync(path.join(changeDir, 'proposal.md')), false, 'proposal.md should be absent for T1');
+  assert.equal(fs.existsSync(path.join(changeDir, 'tasks.md')), false, 'tasks.md should be absent for T1');
+  assert.equal(
+    fs.existsSync(path.join(launchedCwd, 'openspec', 'plan', changeSlug)),
+    false,
+    'T1 codex-agent launch should not create a plan workspace',
+  );
+});
+
+
 test('codex-agent ignores stale repo-local starter shims and keeps the visible checkout stable', () => {
   const repoDir = initRepo();
   seedCommit(repoDir);
@@ -179,7 +246,7 @@ test('codex-agent ignores stale repo-local starter shims and keeps the visible c
 
   const cwdMarker = path.join(repoDir, '.codex-agent-cwd-fallback');
   const argsMarker = path.join(repoDir, '.codex-agent-args-fallback');
-  const launch = runCodexAgent(['fallback-task', 'planner', 'dev', '--model', 'gpt-5.4-mini'], repoDir, {
+  const launch = runCodexAgent(['--tier', 'T3', 'fallback-task', 'planner', 'dev', '--model', 'gpt-5.4-mini'], repoDir, {
     PATH: `${fakeBin}:${process.env.PATH}`,
     GUARDEX_TEST_CODEX_CWD: cwdMarker,
     GUARDEX_TEST_CODEX_ARGS: argsMarker,
diff --git a/test/vscode-active-agents-session-state.test.js b/test/vscode-active-agents-session-state.test.js
index 24da325..2d4c517 100644
--- a/test/vscode-active-agents-session-state.test.js
+++ b/test/vscode-active-agents-session-state.test.js
@@ -383,6 +383,12 @@ test('agent-session-state writes and removes active session records', () => {
     String(process.pid),
     '--cli',
     'codex',
+    '--task-mode',
+    'caveman',
+    '--openspec-tier',
+    'T1',
+    '--routing-reason',
+    'explicit lightweight prefix',
   ]);
   assert.equal(start.status, 0, start.stderr);
 
@@ -395,10 +401,15 @@ test('agent-session-state writes and removes active session records', () => {
   assert.equal(parsed.taskName, 'demo-task');
   assert.equal(parsed.agentName, 'codex');
   assert.equal(parsed.worktreePath, worktreePath);
+  assert.equal(parsed.taskMode, 'caveman');
+  assert.equal(parsed.openspecTier, 'T1');
+  assert.equal(parsed.taskRoutingReason, 'explicit lightweight prefix');
 
   const sessions = sessionSchema.readActiveSessions(tempRoot);
   assert.equal(sessions.length, 1);
   assert.equal(sessions[0].label, 'agent__codex__demo-task');
+  assert.equal(sessions[0].taskMode, 'caveman');
+  assert.equal(sessions[0].openspecTier, 'T1');
 
   const stop = runNode(sessionScript, [
     'stop',
diff --git a/vscode/guardex-active-agents/session-schema.js b/vscode/guardex-active-agents/session-schema.js
index e9282a0..fd4feca 100644
--- a/vscode/guardex-active-agents/session-schema.js
+++ b/vscode/guardex-active-agents/session-schema.js
@@ -35,6 +35,16 @@ function toPositiveInteger(value) {
   return Number.isInteger(normalized) && normalized > 0 ? normalized : null;
 }
 
+function normalizeTaskMode(value) {
+  const normalized = toNonEmptyString(value).toLowerCase();
+  return normalized === 'caveman' || normalized === 'omx' ? normalized : '';
+}
+
+function normalizeOpenSpecTier(value) {
+  const normalized = toNonEmptyString(value).toUpperCase();
+  return ['T0', 'T1', 'T2', 'T3'].includes(normalized) ? normalized : '';
+}
+
 function sanitizeBranchForFile(branch) {
   const normalized = toNonEmptyString(branch, 'session');
   return normalized.replace(/[^a-zA-Z0-9._-]+/g, '__').replace(/^_+|_+$/g, '') || 'session';
@@ -420,6 +430,9 @@ function buildSessionRecord(input) {
     worktreePath,
     pid,
     cliName: toNonEmptyString(input.cliName, 'codex'),
+    taskMode: normalizeTaskMode(input.taskMode),
+    openspecTier: normalizeOpenSpecTier(input.openspecTier),
+    taskRoutingReason: toNonEmptyString(input.taskRoutingReason),
     startedAt: startedAt.toISOString(),
   };
 }
@@ -456,6 +469,9 @@ function normalizeSessionRecord(input, options = {}) {
     worktreePath: path.resolve(worktreePath),
     pid,
     cliName: toNonEmptyString(input.cliName, 'codex'),
+    taskMode: normalizeTaskMode(input.taskMode),
+    openspecTier: normalizeOpenSpecTier(input.openspecTier),
+    taskRoutingReason: toNonEmptyString(input.taskRoutingReason),
     startedAt: startedAt.toISOString(),
     filePath: toNonEmptyString(options.filePath),
     label: deriveSessionLabel(branch, worktreePath),