diff --git a/lib/hire-agent.sh b/lib/hire-agent.sh
index 49ab8ae..2bbea63 100644
--- a/lib/hire-agent.sh
+++ b/lib/hire-agent.sh
@@ -229,6 +229,37 @@ disinto_hire_an_agent() {
     export "${pass_var}=${user_pass}"
   fi
 
+  # Step 1.6: Add the new agent as a write collaborator on the project repo (#856).
+  # Without this, PATCH /issues/{n} {assignees:[agent]} returns 403 Forbidden and
+  # the dev-agent polls forever logging "claim lost to <none> — skipping" (see
+  # issue_claim()'s post-PATCH verify).  Mirrors the collaborator setup applied
+  # to the canonical bot users in lib/forge-setup.sh.  Idempotent: Forgejo's PUT
+  # returns 204 whether the user is being added for the first time or already a
+  # collaborator at the same permission.
+  if [ -n "${FORGE_REPO:-}" ]; then
+    echo ""
+    echo "Step 1.6: Adding '${agent_name}' as write collaborator on '${FORGE_REPO}'..."
+    local collab_code
+    collab_code=$(curl -s -o /dev/null -w '%{http_code}' -X PUT \
+      -H "Authorization: token ${admin_token}" \
+      -H "Content-Type: application/json" \
+      "${forge_url}/api/v1/repos/${FORGE_REPO}/collaborators/${agent_name}" \
+      -d '{"permission":"write"}')
+    case "$collab_code" in
+      204|201|200)
+        echo "  ${agent_name} is a write collaborator on ${FORGE_REPO} (HTTP ${collab_code})"
+        ;;
+      *)
+        echo "  Warning: failed to add '${agent_name}' as collaborator on '${FORGE_REPO}' (HTTP ${collab_code})" >&2
+        echo "  The agent will not be able to claim issues until this is fixed." >&2
+        ;;
+    esac
+  else
+    echo ""
+    echo "Step 1.6: FORGE_REPO not set — skipping collaborator step" >&2
+    echo "  Warning: the agent will not be able to claim issues on the project repo" >&2
+  fi
+
   # Step 2: Create .profile repo on Forgejo
   echo ""
   echo "Step 2: Creating '${agent_name}/.profile' repo (if not exists)..."
diff --git a/lib/issue-lifecycle.sh b/lib/issue-lifecycle.sh
index 80f9afa..1ad3239 100644
--- a/lib/issue-lifecycle.sh
+++ b/lib/issue-lifecycle.sh
@@ -126,11 +126,21 @@ issue_claim() {
   # Assign to self BEFORE adding in-progress label (issue #471).
   # This ordering ensures the assignee is set by the time other pollers
   # see the in-progress label, reducing the stale-detection race window.
-  curl -sf -X PATCH \
+  #
+  # Capture the HTTP status instead of silently swallowing failures (#856).
+  # A 403 here means the bot user is not a write collaborator on the repo —
+  # previously the silent failure fell through to the post-PATCH verify which
+  # only reported "claim lost to <none>", hiding the real root cause.
+  local patch_code
+  patch_code=$(curl -s -o /dev/null -w '%{http_code}' -X PATCH \
     -H "Authorization: token ${FORGE_TOKEN}" \
     -H "Content-Type: application/json" \
     "${FORGE_API}/issues/${issue}" \
-    -d "{\"assignees\":[\"${me}\"]}" >/dev/null 2>&1 || return 1
+    -d "{\"assignees\":[\"${me}\"]}")
+  if [ "$patch_code" != "201" ] && [ "$patch_code" != "200" ]; then
+    _ilc_log "issue #${issue} PATCH assignee failed: HTTP ${patch_code} (403 = missing write collaborator permission on ${FORGE_REPO:-repo})"
+    return 1
+  fi
 
   # Verify the PATCH stuck.  Forgejo's assignees PATCH is last-write-wins, so
   # under concurrent claims from multiple dev agents two invocations can both
diff --git a/tests/lib-issue-claim.bats b/tests/lib-issue-claim.bats
index d7a2c91..85bcc83 100644
--- a/tests/lib-issue-claim.bats
+++ b/tests/lib-issue-claim.bats
@@ -52,12 +52,13 @@ setup() {
   # canned responses per endpoint. Every call gets logged as
   # `METHOD URL` (one line) to $CALLS_LOG for later grep-based asserts.
   curl() {
-    local method="GET" url="" arg
+    local method="GET" url="" arg want_code=""
     while [ $# -gt 0 ]; do
       arg="$1"
       case "$arg" in
         -X) method="$2"; shift 2 ;;
         -H|-d|--data-binary|-o) shift 2 ;;
+        -w) want_code="$2"; shift 2 ;;
         -sf|-s|-f|--silent|--fail) shift ;;
         *) url="$arg"; shift ;;
       esac
@@ -89,7 +90,13 @@ setup() {
         fi
         ;;
       "PATCH ${FORGE_API}/issues/"*)
-        : # accept any PATCH; body is ignored by the mock
+        # Accept any PATCH; body ignored. When caller asked for the HTTP
+        # status via `-w '%{http_code}'` (issue_claim does this since #856
+        # to surface 403s from missing collaborator permission), emit the
+        # code configured by the scenario (default 200).
+        if [ "$want_code" = '%{http_code}' ]; then
+          printf '%s' "${MOCK_PATCH_CODE:-200}"
+        fi
         ;;
       "GET ${FORGE_API}/labels")
         printf '[]'
@@ -165,6 +172,28 @@ count_calls() {
   [ "$(count_calls GET "${FORGE_API}/labels")" -eq 0 ]
 }
 
+# ── PATCH HTTP error surfacing (#856) ───────────────────────────────────────
+
+@test "issue_claim logs specific HTTP code on PATCH failure (403 = missing collaborator)" {
+  export MOCK_ME="bot"
+  export MOCK_INITIAL_ASSIGNEE=""
+  export MOCK_RECHECK_ASSIGNEE=""
+  export MOCK_PATCH_CODE="403"
+
+  run issue_claim 42
+  [ "$status" -eq 1 ]
+
+  # The new log message names the HTTP code explicitly — without this,
+  # a missing-collaborator setup (#856) falls through to the post-PATCH
+  # verify and masquerades as "claim lost to <none>".
+  [[ "$output" == *"PATCH assignee failed: HTTP 403"* ]]
+
+  # No re-read on PATCH failure (we bail before reaching the verify step).
+  [ "$(count_calls GET "${FORGE_API}/issues/42")" -eq 1 ]
+  [ "$(count_calls PATCH "${FORGE_API}/issues/42")" -eq 1 ]
+  [ "$(count_calls POST "${FORGE_API}/issues/42/labels")" -eq 0 ]
+}
+
 # ── pre-check skip ──────────────────────────────────────────────────────────
 
 @test "issue_claim skips early (no PATCH) when pre-check shows another assignee" {