diff --git a/.agents/skills/secondmate-provisioning/SKILL.md b/.agents/skills/secondmate-provisioning/SKILL.md
index 9d5a27e2eff..cc123ffc6a5 100644
--- a/.agents/skills/secondmate-provisioning/SKILL.md
+++ b/.agents/skills/secondmate-provisioning/SKILL.md
@@ -85,6 +85,7 @@ Release happens only on explicit retirement or seed rollback, never on routine r
 
 `bin/fm-home-seed.sh` copies the charter into the secondmate home as `data/charter.md`.
 It also writes the gitignored `.fm-secondmate-parent` durable binding before the required `.fm-secondmate-home` identity marker; the parser header in [`bin/fm-secondmate-parent-lib.sh`](../../../bin/fm-secondmate-parent-lib.sh) owns the record contract, and both files must remain in place.
+Each newly cloned project is also pointed at a treehouse pool root private to its home; [`bin/fm-treehouse-pool-lib.sh`](../../../bin/fm-treehouse-pool-lib.sh)'s header owns the derivation and what a project that already tracks its own `treehouse.toml` triggers.
 `bin/fm-spawn.sh --secondmate` launches it through the secondmate harness path, resolving `config/secondmate-harness` -> `config/crew-harness` -> the primary's own harness unless an explicit per-spawn harness override is passed.
 
 `config/secondmate-harness` may also pin a concrete model and effort for the secondmate agent, in the SAME file rather than a new one: the format is a single whitespace-separated line `<harness> [<model>] [<effort>]`, with only the first non-empty, non-comment line parsed.
diff --git a/bin/fm-home-seed.sh b/bin/fm-home-seed.sh
index 6693ab1df74..658c3269115 100755
--- a/bin/fm-home-seed.sh
+++ b/bin/fm-home-seed.sh
@@ -8,7 +8,10 @@
 #       leases the worktree under the secondmate <id> so the home survives with
 #       no live process and is never recycled until the lease is released with
 #       "treehouse return". Projects are cloned
-#       from the active home into the secondmate home's projects/ directory.
+#       from the active home into the secondmate home's projects/ directory, and
+#       each new clone is pointed at a treehouse pool private to this home (see
+#       bin/fm-treehouse-pool-lib.sh, which owns the derivation and the
+#       project-owned treehouse.toml case).
 #       That project list is non-exclusive provisioning data. Pass --no-projects
 #       instead of a project list to seed a project-less home for a domain whose
 #       subject is the firstmate repo itself; it is mutually exclusive with a
@@ -49,6 +52,8 @@ SUB_HOME_PARENT_MARKER=".fm-secondmate-parent"
 . "$SCRIPT_DIR/fm-secondmate-charter-lib.sh"
 # shellcheck source=bin/fm-wake-lib.sh
 . "$SCRIPT_DIR/fm-wake-lib.sh"
+# shellcheck source=bin/fm-treehouse-pool-lib.sh
+. "$SCRIPT_DIR/fm-treehouse-pool-lib.sh"
 
 usage() {
   echo "usage: fm-home-seed.sh <id> <home|-> {<project>...|--no-projects}" >&2
@@ -482,6 +487,7 @@ EOF
   fi
   url=$(source_origin_url "$project" "$mode" "$src") || return 1
   git clone --quiet "$url" "$dst"
+  fm_treehouse_configure_pool_root "$dst" "$home"
 }
 
 validate_seed_project() {
diff --git a/bin/fm-remote-home-provision.sh b/bin/fm-remote-home-provision.sh
index 8f733d6d3c4..1555889f1ea 100755
--- a/bin/fm-remote-home-provision.sh
+++ b/bin/fm-remote-home-provision.sh
@@ -14,7 +14,10 @@
 # "remote" - read by bin/fm-teardown.sh's cleanup gate so a delegated public
 # reply promise, which the subsystem can only carry on the parent's own
 # filesystem, is never mistaken for one this child could hold - and the
-# .fm-secondmate-home marker commits the complete seed last.
+# .fm-secondmate-home marker commits the complete seed last. Each newly cloned
+# project is also pointed at a treehouse pool private to this home through
+# bin/fm-treehouse-pool-lib.sh, which owns the derivation and the project-owned
+# treehouse.toml case.
 # A newly created home is removed on failure. An existing matching seeded home
 # is converged only through guarded ordinary-file updates and new project clones.
 set -eu
@@ -26,6 +29,8 @@ MAX_MANIFEST_BYTES=1048576
 
 # shellcheck source=bin/fm-project-origin-lib.sh
 . "$SCRIPT_DIR/fm-project-origin-lib.sh"
+# shellcheck source=bin/fm-treehouse-pool-lib.sh
+. "$SCRIPT_DIR/fm-treehouse-pool-lib.sh"
 
 die() { printf 'error: %s\n' "$1" >&2; exit 1; }
 
@@ -230,6 +235,7 @@ EOF
   else
     printf '%s\n' "$NAME" >> "$CREATED_PROJECTS"
     git clone --quiet -- "$ORIGIN" "$DEST" || die "could not clone project $NAME on the remote host"
+    fm_treehouse_configure_pool_root "$DEST" "$FM_HOME" || die "could not configure treehouse pool root for project $NAME"
     if [ "$MODE" = no-mistakes ]; then
       command -v no-mistakes >/dev/null 2>&1 || die "no-mistakes is unavailable for project $NAME"
       (cd "$DEST" && no-mistakes init >/dev/null && no-mistakes doctor >/dev/null) \
diff --git a/bin/fm-test-run.sh b/bin/fm-test-run.sh
index e69855f3875..3c9de2d123c 100755
--- a/bin/fm-test-run.sh
+++ b/bin/fm-test-run.sh
@@ -311,7 +311,7 @@ family_for_basename() {
     fm-backend-herdr-agent-exit-shell-e2e.test.sh|\
     fm-herdr-attached-viewer-live-e2e.test.sh|fm-herdr-session-cleanup-e2e.test.sh|\
     fm-backend-herdr-smoke.test.sh|fm-backend-herdr-workspace-per-home-e2e.test.sh|\
-    fm-control-herdr-smoke.test.sh)
+    fm-control-herdr-smoke.test.sh|fm-treehouse-pool-lib.test.sh)
       printf '%s\n' real-herdr-gated
       ;;
     fm-backlog-handoff.test.sh|fm-on.test.sh|fm-remote-backlog-handoff.test.sh|\
diff --git a/bin/fm-treehouse-pool-lib.sh b/bin/fm-treehouse-pool-lib.sh
new file mode 100755
index 00000000000..c19c3dda967
--- /dev/null
+++ b/bin/fm-treehouse-pool-lib.sh
@@ -0,0 +1,57 @@
+#!/usr/bin/env bash
+# fm-treehouse-pool-lib.sh - point a freshly cloned project's treehouse
+# worktree pool at a root private to the home that cloned it.
+#
+# WHY: treehouse names a project's pool from a hash of the origin URL alone,
+# placed under its configured root (default $HOME). Two firstmate homes that
+# each clone the same origin therefore collide on one pool, and every
+# worktree in it stays linked to whichever clone created it first - so a
+# secondmate spawning work in a project its parent home also clones gets
+# handed a worktree of the PARENT's clone. fm-spawn.sh's pre-registration
+# guard (bin/fm-claude-trust.sh, bin/fm-agy-trust.sh) already catches and
+# refuses that mismatch; this removes the collision instead of relaxing the
+# guard. Treehouse reads treehouse.toml from a project's own repository root
+# and honors a `root` key there ({root}/.treehouse/ instead of $HOME).
+#
+# The root is derived from the home's absolute path and lives in the machine
+# state directory, outside the home worktree and every other git repository:
+# treehouse keeps its pool out of git by appending the pool path to the
+# .gitignore of whichever repository encloses {root}/.treehouse, so a root
+# inside the home (itself a firstmate clone) would leave that home dirty and
+# stop its fast-forward updates.
+
+# fm_treehouse_pool_root <home>
+# Prints the stable, collision-free pool root for <home>.
+fm_treehouse_pool_root() {
+  local home=$1 base hash
+  base="${XDG_STATE_HOME:-$HOME/.local/state}/firstmate/treehouse-pools"
+  if command -v shasum >/dev/null 2>&1; then
+    hash=$(printf '%s' "$home" | shasum -a 256 | awk '{print $1}')
+  elif command -v sha256sum >/dev/null 2>&1; then
+    hash=$(printf '%s' "$home" | sha256sum | awk '{print $1}')
+  else
+    hash=$(printf '%s' "$home" | cksum | awk '{printf "%08x%08x", $1, $2}')
+  fi
+  printf '%s/%s\n' "$base" "$hash"
+}
+
+# fm_treehouse_configure_pool_root <clone-dir> <home>
+# Points <clone-dir>'s treehouse pool at <home>'s own pool root and excludes
+# the generated file locally so the clone stays clean. A project that tracks
+# its own treehouse.toml keeps it: the seed warns and continues instead of
+# aborting.
+fm_treehouse_configure_pool_root() {
+  local clone=$1 home=$2 toml exclude pool_root
+  toml="$clone/treehouse.toml"
+  if git -C "$clone" ls-files --error-unmatch treehouse.toml >/dev/null 2>&1; then
+    echo "warning: project $(basename "$clone") keeps its own treehouse pool configuration in treehouse.toml, so this home's per-home pool root was not applied; worker spawns from this home may be refused if that configuration resolves to a pool shared with another home. Give that configuration a root unique to this home to avoid the collision." >&2
+    return 0
+  fi
+  pool_root=$(fm_treehouse_pool_root "$home")
+  printf 'root = "%s"\n' "$pool_root" > "$toml.tmp.$$"
+  mv -f -- "$toml.tmp.$$" "$toml"
+  exclude="$clone/.git/info/exclude"
+  mkdir -p "$(dirname "$exclude")"
+  touch "$exclude"
+  grep -qxF '/treehouse.toml' "$exclude" 2>/dev/null || printf '/treehouse.toml\n' >> "$exclude"
+}
diff --git a/docs/configuration.md b/docs/configuration.md
index d10624d2a77..9b955a5ec25 100644
--- a/docs/configuration.md
+++ b/docs/configuration.md
@@ -277,6 +277,8 @@ The lease is held under the secondmate id until explicit retirement or seed roll
 Teardown of a leased home fails closed if `treehouse return` cannot release the lease; plain-clone homes with no treehouse pool slot are removed directly.
 Secondmate routes cover `no-mistakes` and `direct-PR` projects; `local-only` projects remain main-firstmate work.
 For `no-mistakes` projects, seeding initializes only projects newly cloned into a secondmate home and refuses to mutate a preexisting clone that is not already initialized.
+A project cloned into a secondmate home, local or remote, is also pointed at a treehouse pool root private to that home, so a secondmate's workers lease worktrees linked to the secondmate's own clone rather than to the home the parent cloned from.
+The generated `treehouse.toml` is excluded locally so the clone stays clean, and a project that already tracks its own `treehouse.toml` is left untouched with a named warning that this home's per-home pool root was not applied and that worker spawns from this home may be refused if that configuration resolves to a pool shared with another home; [`bin/fm-treehouse-pool-lib.sh`](../bin/fm-treehouse-pool-lib.sh)'s header owns the pool-root derivation.
 After creating a secondmate, move existing main-backlog queued items that you have judged in-scope with `fm-backlog-handoff.sh <secondmate-id> <item-key>...`; it refuses In flight, Done, or non-secondmate homes, and its [script header](../bin/fm-backlog-handoff.sh) owns route-specific wake outcomes and retries.
 Set `FM_SECONDMATE_CHARTER` to seed from inline charter text when no filled charter brief exists; set `FM_SECONDMATE_SCOPE` when the routing scope should differ from the charter text.
 The seeded home's `data/charter.md` owns the standard secondmate lifecycle and escalation contract; the route file points to it through the existing `home:` field instead of adding another pointer.
diff --git a/tests/fm-treehouse-pool-lib.test.sh b/tests/fm-treehouse-pool-lib.test.sh
new file mode 100755
index 00000000000..2a5d065e7e8
--- /dev/null
+++ b/tests/fm-treehouse-pool-lib.test.sh
@@ -0,0 +1,139 @@
+#!/usr/bin/env bash
+# tests/fm-treehouse-pool-lib.test.sh - proves fm_treehouse_configure_pool_root
+# (bin/fm-treehouse-pool-lib.sh) actually gives two clones of one origin their
+# own treehouse worktree pools without dirtying either home, using the real
+# treehouse binary end to end (harness-dependent check: the pool-collision
+# behavior this fixes is treehouse's own, so a mocked path computation would
+# only confirm the assumption already written into the mock). Skips when
+# treehouse is absent.
+set -u
+
+# shellcheck source=tests/lib.sh
+. "$(dirname "${BASH_SOURCE[0]}")/lib.sh"
+
+command -v treehouse >/dev/null 2>&1 || { echo "skip: treehouse not found"; exit 0; }
+
+# shellcheck source=/dev/null
+. "$ROOT/bin/fm-treehouse-pool-lib.sh"
+
+TMP_ROOT=$(fm_test_tmproot fm-treehouse-pool-lib) || fail "could not create temp root"
+# Keep the derived pool roots inside the fixture instead of the developer's
+# machine state directory. The fixture root is not a git repository, so a
+# pool root here proves the pool can live outside every repository.
+export XDG_STATE_HOME="$TMP_ROOT/state"
+# Contain treehouse's own state, and any fallback to its default $HOME pool, in
+# the fixture rather than the developer's home directory.
+export HOME="$TMP_ROOT/user-home"
+mkdir -p "$HOME"
+
+# A realistic firstmate home: a real git repository that ignores its project
+# clones, exactly as a seeded secondmate home does, so a pool root that dirties
+# the home surfaces in its own `git status`.
+make_home() {
+  local home=$1
+  fm_git_init_commit "$home"
+  printf 'projects/\n' > "$home/.gitignore"
+  git -C "$home" add .gitignore
+  git -C "$home" -c user.name='Firstmate Tests' -c user.email='tests@example.invalid' commit -qm gitignore
+}
+
+# One throwaway origin, cloned twice - standing in for a project two separate
+# firstmate homes have each cloned.
+fm_git_init_commit "$TMP_ROOT/widget-origin"
+fm_git_add_origin "$TMP_ROOT/widget-origin" "$TMP_ROOT/widget-origin.git"
+make_home "$TMP_ROOT/home-a"
+make_home "$TMP_ROOT/home-b"
+git clone --quiet "$TMP_ROOT/widget-origin.git" "$TMP_ROOT/home-a/projects/widget" || fail "could not clone home A's widget"
+git clone --quiet "$TMP_ROOT/widget-origin.git" "$TMP_ROOT/home-b/projects/widget" || fail "could not clone home B's widget"
+
+WT_A=; WT_B=
+cleanup_leases() {
+  [ -z "$WT_A" ] || treehouse return --force "$WT_A" >/dev/null 2>&1
+  [ -z "$WT_B" ] || treehouse return --force "$WT_B" >/dev/null 2>&1
+  fm_test_cleanup
+}
+trap cleanup_leases EXIT
+
+fm_treehouse_configure_pool_root "$TMP_ROOT/home-a/projects/widget" "$TMP_ROOT/home-a" \
+  || fail "fm_treehouse_configure_pool_root refused for home A"
+fm_treehouse_configure_pool_root "$TMP_ROOT/home-b/projects/widget" "$TMP_ROOT/home-b" \
+  || fail "fm_treehouse_configure_pool_root refused for home B"
+pass "fm_treehouse_configure_pool_root accepts two fresh clones of one origin"
+
+[ -z "$(git -C "$TMP_ROOT/home-a/projects/widget" status --porcelain)" ] \
+  || fail "home A's clone reads as dirty after configuring its pool root"
+[ -z "$(git -C "$TMP_ROOT/home-b/projects/widget" status --porcelain)" ] \
+  || fail "home B's clone reads as dirty after configuring its pool root"
+pass "the generated treehouse.toml is excluded locally, so both clones stay clean"
+
+# A project that tracks its own treehouse.toml keeps its own pool
+# configuration; the seed must warn instead of aborting, and the file must be
+# left untouched.
+fm_git_init_commit "$TMP_ROOT/owned-origin"
+printf 'root = "/srv/owned"\n' > "$TMP_ROOT/owned-origin/treehouse.toml"
+git -C "$TMP_ROOT/owned-origin" add treehouse.toml
+git -C "$TMP_ROOT/owned-origin" -c user.name='Firstmate Tests' -c user.email='tests@example.invalid' commit -qm owned
+fm_git_add_origin "$TMP_ROOT/owned-origin" "$TMP_ROOT/owned-origin.git"
+git clone --quiet "$TMP_ROOT/owned-origin.git" "$TMP_ROOT/home-a/projects/owned" || fail "could not clone home A's owned project"
+warning=$(fm_treehouse_configure_pool_root "$TMP_ROOT/home-a/projects/owned" "$TMP_ROOT/home-a" 2>&1) \
+  || fail "fm_treehouse_configure_pool_root aborted the seed on a project-owned treehouse.toml"
+[ "$(cat "$TMP_ROOT/home-a/projects/owned/treehouse.toml")" = 'root = "/srv/owned"' ] \
+  || fail "fm_treehouse_configure_pool_root overwrote a project-owned treehouse.toml"
+case "$warning" in
+  *"owned"*"treehouse.toml"*"per-home pool root was not applied"*"may be refused"*) : ;;
+  *) fail "fm_treehouse_configure_pool_root did not name the project and file whose pool config it left alone: $warning" ;;
+esac
+pass "a project-owned treehouse.toml is left untouched with a named warning, not a seed abort"
+
+ROOT_A=$(fm_treehouse_pool_root "$TMP_ROOT/home-a")
+ROOT_B=$(fm_treehouse_pool_root "$TMP_ROOT/home-b")
+[ "$ROOT_A" != "$ROOT_B" ] || fail "the two homes derived the same pool root '$ROOT_A'"
+
+WT_A=$(cd "$TMP_ROOT/home-a/projects/widget" && treehouse get --lease --lease-holder home-a) \
+  || fail "treehouse get --lease failed for home A"
+[ -n "$WT_A" ] || fail "treehouse get --lease did not report a worktree path for home A"
+case "$WT_A" in
+  "$ROOT_A"/.treehouse/*) : ;;
+  *) fail "home A's worktree '$WT_A' is not under home A's configured pool root '$ROOT_A'" ;;
+esac
+GITDIR_A=$(cat "$WT_A/.git")
+case "$GITDIR_A" in
+  *"$TMP_ROOT/home-a/projects/widget/.git/worktrees/"*) : ;;
+  *) fail "home A's pooled worktree links back to the wrong clone: $GITDIR_A" ;;
+esac
+POOL_A=$(dirname "$(dirname "$WT_A")")
+
+# Return A before B acquires: against a shared pool treehouse hands B the exact
+# slot A just freed, which is the reuse path that would hand a secondmate a
+# parent-owned worktree. Releasing A first makes the pool comparison below fail
+# if the two clones still resolve to one pool.
+treehouse return --force "$WT_A" >/dev/null 2>&1 || fail "could not return home A's leased worktree before home B acquires"
+WT_A=
+
+WT_B=$(cd "$TMP_ROOT/home-b/projects/widget" && treehouse get --lease --lease-holder home-b) \
+  || fail "treehouse get --lease failed for home B"
+[ -n "$WT_B" ] || fail "treehouse get --lease did not report a worktree path for home B"
+case "$WT_B" in
+  "$ROOT_B"/.treehouse/*) : ;;
+  *) fail "home B's worktree '$WT_B' is not under home B's configured pool root '$ROOT_B'" ;;
+esac
+GITDIR_B=$(cat "$WT_B/.git")
+case "$GITDIR_B" in
+  *"$TMP_ROOT/home-b/projects/widget/.git/worktrees/"*) : ;;
+  *) fail "home B's pooled worktree links back to the wrong clone: $GITDIR_B" ;;
+esac
+POOL_B=$(dirname "$(dirname "$WT_B")")
+[ "$POOL_A" != "$POOL_B" ] || fail "both homes resolved to the same treehouse pool '$POOL_A'"
+pass "each clone acquires from its own pool, even after the first home returns its slot"
+
+# The regression this fixes: treehouse keeps a pool out of git by rewriting the
+# .gitignore of the repository enclosing {root}/.treehouse, so a root inside a
+# home leaves that home permanently dirty and disables its fast-forward updates.
+[ -z "$(git -C "$TMP_ROOT/home-a" status --porcelain)" ] \
+  || fail "home A reads as dirty after an acquire"
+[ -z "$(git -C "$TMP_ROOT/home-b" status --porcelain)" ] \
+  || fail "home B reads as dirty after an acquire"
+pass "neither home's own repository is dirtied by a project's pool acquire"
+
+treehouse return --force "$WT_B" >/dev/null 2>&1 || fail "could not return home B's leased worktree"
+WT_A=; WT_B=