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/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(),