CB-523 (opencode): generated worker config pins compaction.auto

A worker that exhausts its context dies mid-turn and its bridge_reply — the
whole point of the turn — dies with it. Auto-compaction is a condition of the
turn contract for a spawned peer, not an operator preference.

OPENCODE_CONFIG is merged over ~/.config/opencode/config.json rather than
replacing it, so workers already inherited auto:true from the home file. That
inheritance is exactly what this removes as a dependency: the home file is
outside this repo, differs per machine, and is not ours to rely on.

The trade is recorded in the code: an OPENCODE_CONFIG value overrides the home
value, so an operator cannot disable compaction for bridged workers from home.
Deliberate for peers we spawn and whose turns we must land; per-profile control
would be a profile knob, not the removal of this line.

Origin: fleet-wide auto-compaction audit by peer lead gpt-sol-5.6, which found
autoCompactEnabled:false alongside a 300k window across the Claude instance
configs. Handed over uncommitted; taken deliberately, with rationale added.

bridged/src/main/java/dev/ltms/bridged/worker/OpenCodeLauncher.java

@@ -247,6 +247,21 @@ public final class OpenCodeLauncher extends HerdrPeerLauncher {
 
             ObjectNode root = JSON.createObjectNode();
             root.put("$schema", "https://opencode.ai/config.json");
+            // CB-523, opencode side: a worker that runs out of context dies mid-turn, and its reply
+            // — the entire point of the turn — is lost with it. Auto-compaction is therefore not an
+            // operator preference for a bridged worker, it is a condition of the turn contract.
+            //
+            // Stated deliberately even though it is redundant today: OPENCODE_CONFIG is MERGED over
+            // ~/.config/opencode/config.json rather than replacing it, so a worker already inherits
+            // an `auto: true` set at home. We do not want that inheritance to be what the guarantee
+            // rests on — the home file is outside this repo, differs per machine, and is not ours.
+            //
+            // Know the cost before removing it: this key WINS over the home config (verified — an
+            // OPENCODE_CONFIG value overrides the home value, it does not defer to it), so an
+            // operator who sets `compaction.auto: false` at home cannot turn it off for bridged
+            // workers. That is the intended trade for peers we spawn and whose turns we must land;
+            // if per-profile control is ever wanted, add a profile knob rather than dropping this.
+            root.putObject("compaction").put("auto", true);
 
             if (cfg.hasMcp()) {
                 Path charter = dir.resolve("reply-charter.md");

bridged/src/test/java/dev/ltms/bridged/worker/OpenCodeLauncherTest.java

@@ -74,6 +74,8 @@ class OpenCodeLauncherTest {
         // Assert on parsed structure, not substrings: the generated config is real JSON and its
         // whitespace is the formatter's business, not the contract's.
         JsonNode json = new ObjectMapper().readTree(Path.of(cfgPath).toFile());
+        assertTrue(json.path("compaction").path("auto").asBoolean(),
+                "spawned opencode peers explicitly enable automatic compaction");
         JsonNode bridge = json.path("mcp").path("bridge");
         assertEquals("remote", bridge.path("type").asText(), "bridge is mounted as a remote MCP server");
         assertEquals("http://127.0.0.1:8765/mcp", bridge.path("url").asText(),