Merge branch 'feat/subagent-report-semantics' into feat/subagent-settlement-delivery

# Conflicts:
#	examples/acp-agent/tests/snapshots/advanced-toolchain/session.1.jsonl
#	examples/acp-agent/tests/snapshots/advanced-toolchain/session.2.jsonl
#	examples/acp-agent/tests/snapshots/subagent-depth-two-rejection/session.1.jsonl
#	examples/acp-agent/tests/snapshots/subagent-depth-two-rejection/session.2.jsonl
#	examples/acp-agent/tests/snapshots/subagent-mixed/session.1.jsonl
#	examples/acp-agent/tests/snapshots/subagent-mixed/session.2.jsonl
#	examples/acp-agent/tests/snapshots/subagent-multi/session.1.jsonl
#	examples/acp-agent/tests/snapshots/subagent-multi/session.2.jsonl
#	examples/headless-agent/tests/snapshots/advanced-toolchain/session.1.jsonl
#	examples/headless-agent/tests/snapshots/advanced-toolchain/session.2.jsonl
#	examples/headless-agent/tests/snapshots/advanced-toolchain/session.jsonl
#	examples/headless-agent/tests/snapshots/compaction-recovery/session.jsonl
#	examples/headless-agent/tests/snapshots/pty-tools/session.jsonl

examples/acp-agent/tests/snapshots/read-image/tool-schemas.expected.json

@@ -272,7 +272,7 @@
     },
     {
       "name": "subagent_fork",
-      "description": "Delegate a task to a subagent that inherits this conversation: a child agent seeded with all completed turns so far (it does not see the current in-flight turn), returning only its final result. Use this when the subtask builds on this conversation's context — a follow-up analysis, a review, a continuation — without consuming this conversation's context for the work itself. You receive only its final answer, not its intermediate steps. Set `run_in_background: true` to start a background subagent that keeps its conversation: you receive only its subagent id, never its result, and it works on its own. Use this for work whose result you do not need returned by this call; `send_message` sends it more work.",
+      "description": "Delegate a task to a subagent that inherits this conversation: a child agent seeded with all completed turns so far (it does not see the current in-flight turn), returning only its final result. Use this when the subtask builds on this conversation's context — a follow-up analysis, a review, a continuation — without consuming this conversation's context for the work itself. You receive only its final answer, not its intermediate steps.",
       "parameters": {
         "type": "object",
         "properties": {
@@ -283,10 +283,6 @@
           "prompt": {
             "type": "string",
             "description": "The task for the subagent. It already sees this conversation's completed turns, so build on them freely and state only what is new."
-          },
-          "run_in_background": {
-            "type": "boolean",
-            "description": "Run as a background subagent that keeps its conversation and return only its subagent id. This call never returns its result; send it more work with send_message."
           }
         },
         "required": [