fix(tmux): preserve sender identity across sockets

Prefer the pane's MOSAIC_AGENT_NAME and query only the local tmux server when falling back, so destination socket holders cannot corrupt reply routing. Add red-first regression coverage for env, local-session, and unknown sender paths.

Co-Authored-By: OpenAI GPT <noreply@openai.com>

docs/scratchpads/808-agent-send-sender-identity.md

@@ -0,0 +1,37 @@
+# Issue #808 — agent-send sender identity
+
+## Objective
+
+Fix cross-socket `agent-send.sh` preambles so replies route to the real sender rather than a destination-socket holder session.
+
+## Scope and acceptance criteria
+
+- Prefer exported `MOSAIC_AGENT_NAME` as the authoritative sender session name.
+- If it is unset, query the sender's local/default tmux socket for `#S` without destination `-L` arguments.
+- Preserve `?` when sender identity cannot be determined.
+- Do not alter destination socket dispatch.
+- Add red-first regressions for all three identity paths.
+
+## Plan
+
+1. Extend `agent-send.test.sh` with deterministic fake-tmux coverage.
+2. Run the test against the unpatched implementation and record RED evidence.
+3. Apply the minimal sender lookup fix only.
+4. Run the focused suite and repository quality gates.
+5. Commit, queue-guard, push, and open an author-only PR for independent review.
+
+## Constraints and risks
+
+- Worker lane is author-only: no self-review or merge.
+- `docs/TASKS.md` and mission state are orchestrator-owned and will not be modified.
+- Pre-existing runtime changes under `.mosaic/orchestrator/` are excluded from this work.
+- Budget: no explicit token cap; keep changes limited to the shell tool, sibling regression test, and this scratchpad.
+
+## Evidence
+
+- RED: `bash packages/mosaic/framework/tools/tmux/agent-send.test.sh` failed on the unpatched implementation with `PASS=12 FAIL=3`; it selected `destination-holder` instead of both `MOSAIC_AGENT_NAME=authoritative-agent` and local session `local-agent`. The genuinely unavailable sender case already exercised and preserved `?`.
+- GREEN: `bash packages/mosaic/framework/tools/tmux/agent-send.test.sh` passed with `PASS=15 FAIL=0`; coverage includes env authority, local/default tmux fallback across a destination `-L`, explicit rejection of the destination holder, and `?` fallback.
+- Syntax: `bash -n packages/mosaic/framework/tools/tmux/agent-send.sh packages/mosaic/framework/tools/tmux/agent-send.test.sh` passed.
+- Quality gates: `pnpm typecheck` (42/42 tasks), `pnpm lint` (23/23 tasks), and `pnpm format:check` all passed after installing the frozen lockfile dependencies. The first install attempt failed because pnpm's configured store pointed at `/root`; retrying with the existing user-owned store (`--store-dir /home/hermes/.local/share/pnpm/store`) succeeded without changing tracked dependency files.
+- Documentation: no public API or operator workflow changed; the source comment, regression-test contract, and this implementation record cover the internal bug fix.
+- Independent review: intentionally pending for the reviewer assigned by `mosaic-100`; this author-only lane will not self-review or merge.

packages/mosaic/framework/tools/tmux/agent-send.sh

@@ -122,12 +122,11 @@ fi
 
 # Source label: this agent's host:session (auto-detected, overridable).
 if [ -z "$SRC_LABEL" ]; then
-  tmux_cmd=(tmux)
-  if [ -n "$SOCKET_NAME" ]; then
-    tmux_cmd+=(-L "$SOCKET_NAME")
-  fi
   src_host=$(hostname -s 2>/dev/null || echo "?")
-  src_sess=$("${tmux_cmd[@]}" display-message -p '#S' 2>/dev/null || echo "?")
+  src_sess=${MOSAIC_AGENT_NAME:-}
+  if [ -z "$src_sess" ]; then
+    src_sess=$(tmux display-message -p '#S' 2>/dev/null || echo "?")
+  fi
   SRC_LABEL="${src_host}:${src_sess}"
 fi
 

packages/mosaic/framework/tools/tmux/agent-send.test.sh

@@ -14,6 +14,9 @@
 #   5. invalid class => exit 3, nothing sent.
 #   6. --class with no value => exit 3.
 #   7. the documented consumer regex parses producer output for every class.
+#   8. MOSAIC_AGENT_NAME is authoritative for sender identity.
+#   9. sender fallback queries local tmux, never the destination -L socket.
+#  10. an undeterminable sender is stamped as "?".
 set -uo pipefail
 
 HERE=$(cd -- "$(dirname -- "$0")" && pwd)
@@ -21,22 +24,45 @@ TOOL="$HERE/agent-send.sh"
 
 # Capture stub: stands in for send-message.sh. Decodes -b and prints the payload.
 STUB=$(mktemp)
-trap 'rm -f "$STUB"' EXIT
+FAKE_BIN=$(mktemp -d)
+trap 'rm -f "$STUB"; rm -rf "$FAKE_BIN"' EXIT
 cat >"$STUB" <<'STUB_EOF'
 #!/usr/bin/env bash
 set -uo pipefail
 b64=""
-while getopts "t:b:r:v" o; do case "$o" in b) b64=$OPTARG ;; *) : ;; esac; done
+while getopts "L:t:b:r:v" o; do case "$o" in b) b64=$OPTARG ;; *) : ;; esac; done
 printf '%s' "$b64" | base64 -d
 STUB_EOF
 chmod +x "$STUB"
 
+# Fake tmux distinguishes the sender's default socket from a destination socket.
+cat >"$FAKE_BIN/tmux" <<'TMUX_EOF'
+#!/usr/bin/env bash
+set -uo pipefail
+case "${FAKE_TMUX_MODE:-sessions}" in
+  unavailable) exit 1 ;;
+  sessions)
+    if [ "${1:-}" = "-L" ]; then
+      printf '%s\n' 'destination-holder'
+    else
+      printf '%s\n' 'local-agent'
+    fi
+    ;;
+esac
+TMUX_EOF
+chmod +x "$FAKE_BIN/tmux"
+
 PASS=0; FAIL=0
 ok()   { PASS=$((PASS+1)); printf 'ok   %s\n' "$1"; }
 no()   { FAIL=$((FAIL+1)); printf 'FAIL %s\n   %s\n' "$1" "$2"; }
 
 # Run the tool with the stub injected; echoes captured payload on stdout.
 run() { AGENT_SEND_SENDER="$STUB" bash "$TOOL" -S a:src -n dsthost "$@"; }
+run_auto() {
+  env -u MOSAIC_AGENT_NAME \
+    AGENT_SEND_SENDER="$STUB" PATH="$FAKE_BIN:$PATH" \
+    bash "$TOOL" -n dsthost "$@"
+}
 
 # Documented consumer grammar — the daemon will mirror exactly this.
 GRAMMAR='^\[(\S+) -> (\S+) class=(terminal-log|actionable|human|reaction)\] (.*)$'
@@ -92,6 +118,30 @@ classic=$(run -s mos -m "plain body")
 [[ "$classic" =~ $GRAMMAR_NOCLASS ]] && [ "${BASH_REMATCH[3]}" = "plain body" ] \
   && ok "grammar (no-class) parses classic line" || no "grammar (no-class) parses classic line" "line=[$classic]"
 
+# 8. Exported pane identity wins even when dispatch targets another tmux socket.
+src_host=$(hostname -s)
+got=$(MOSAIC_AGENT_NAME=authoritative-agent FAKE_TMUX_MODE=sessions \
+  AGENT_SEND_SENDER="$STUB" PATH="$FAKE_BIN:$PATH" \
+  bash "$TOOL" -L destination-socket -n dsthost -s mos -m "env identity")
+want="[$src_host:authoritative-agent -> dsthost:mos] env identity"
+[ "$got" = "$want" ] && ok "MOSAIC_AGENT_NAME is authoritative across sockets" \
+  || no "MOSAIC_AGENT_NAME is authoritative across sockets" "got=[$got] want=[$want]"
+
+# 9. Without the env identity, self-lookup uses local tmux, not destination -L.
+got=$(FAKE_TMUX_MODE=sessions run_auto -L destination-socket -s mos -m "local fallback")
+want="[$src_host:local-agent -> dsthost:mos] local fallback"
+[ "$got" = "$want" ] && ok "cross-socket fallback uses local sender session" \
+  || no "cross-socket fallback uses local sender session" "got=[$got] want=[$want]"
+[[ "$got" != *":destination-holder ->"* ]] \
+  && ok "cross-socket fallback rejects destination holder identity" \
+  || no "cross-socket fallback rejects destination holder identity" "got=[$got]"
+
+# 10. If neither env nor local tmux identifies the sender, preserve '?'.
+got=$(FAKE_TMUX_MODE=unavailable run_auto -L destination-socket -s mos -m "unknown fallback")
+want="[$src_host:? -> dsthost:mos] unknown fallback"
+[ "$got" = "$want" ] && ok "unknown sender falls back to ?" \
+  || no "unknown sender falls back to ?" "got=[$got] want=[$want]"
+
 echo "---"
 echo "PASS=$PASS FAIL=$FAIL"
 [ "$FAIL" -eq 0 ]