fix(#129): mark m[0]/m[1] history prepends synthetic so they don't suppress titles

OpenCode's auto-title generation (SessionPrompt.ensureTitle) only titles a
session when EXACTLY ONE "real" user message exists, where real =
`role === "user" && !parts.every(p => p.synthetic)` — it does NOT check
`ignored`. Magic Context injects its history blocks by prepending two
`role: "user"` messages (m[0] cumulative baseline + m[1] delta) on every
transform — including a brand-new session's first turn, where m[0] is an empty
placeholder and m[1] is minimal. Those parts had no `synthetic` flag, so a fresh
first turn presented THREE real user messages (m0 + m1 + the actual prompt) →
`filter(real).length !== 1` → ensureTitle returned without titling, permanently.

Reproduced in clean OpenCode (no custom build) in Docker: MC-enabled fresh
session never titles ("New session - <ISO>"); plugin-disabled titles fine;
disabling auto-search did NOT help (auto-search only appends text, keeping the
count at 1) — isolating the m[0]/m[1] prepend as the cause. The git-vs-non-git
asymmetry the reporter saw is a timing artifact of the title fiber forking with
the shared, about-to-be-transformed `msgs` array.

Fix: mark all three prepend sites' text parts `synthetic: true` (the two v2
m[0]/m[1] blocks + the v1 `<session-history>` fallback). `synthetic` keeps them
in the real model call — OpenCode's `toModelMessagesEffect` filters on `ignored`,
NOT `synthetic`, so history injection is preserved — while excluding them from
the title gate. `ignored: true` would have been wrong: it strips parts from the
model call and would have removed the injected history from the agent's context.
OpenCode-only; Pi has no equivalent title gate.

Verified in Docker before/after: the two previously-failing fresh-session cases
now title correctly. Prior fix afb19b2 (v0.23.0) only guarded notification posts
and never touched this prepend — which is why the issue persisted.

Co-authored-by: Alfonso [Magic Context] <288211368+alfonso-magic-context@users.noreply.github.com>

Author: ualtinok

packages/plugin/src/hooks/magic-context/inject-compartments.ts

@@ -536,9 +536,12 @@ export function renderCompartmentInjection(
     const firstMessage = messages[0];
     const textPart = firstMessage ? findFirstTextPart(firstMessage.parts) : null;
     if (!firstMessage || !textPart || isDroppedPlaceholder(textPart.text)) {
+        // synthetic: true — injected context, not a real user turn. Keeps it out
+        // of OpenCode's auto-title gate (issue #129) while still reaching the
+        // model (toModelMessagesEffect filters `ignored`, not `synthetic`).
         messages.unshift({
             info: { role: "user", sessionID: sessionId },
-            parts: [{ type: "text", text: historyBlock }],
+            parts: [{ type: "text", text: historyBlock, synthetic: true }],
         });
     } else {
         textPart.text = `${historyBlock}\n\n${textPart.text}`;
@@ -2169,14 +2172,29 @@ function prependM0M1Messages(
     m0Text: string,
     m1Text: string,
 ): void {
+    // `synthetic: true` marks these as injected context, not real user turns.
+    // OpenCode's `toModelMessagesEffect` filters on `ignored` (NOT `synthetic`),
+    // so the blocks STILL reach the model — but its title-generation gate
+    // (`ensureTitle`) counts a message as a real user turn only when not every
+    // part is synthetic, and skips titling unless exactly one real user message
+    // exists. Without this flag, m[0]+m[1] add two phantom user turns on the
+    // first message and permanently suppress the session's auto-title (issue
+    // #129). Must NOT use `ignored` here — that would strip the history
+    // injection from the real model call.
     messages.unshift(
         {
             info: { role: "user", sessionID: sessionId },
-            parts: [{ type: "text", text: m0Text.length > 0 ? m0Text : M0_EMPTY_BODY }],
+            parts: [
+                {
+                    type: "text",
+                    text: m0Text.length > 0 ? m0Text : M0_EMPTY_BODY,
+                    synthetic: true,
+                },
+            ],
         },
         {
             info: { role: "user", sessionID: sessionId },
-            parts: [{ type: "text", text: m1Text }],
+            parts: [{ type: "text", text: m1Text, synthetic: true }],
         },
     );
 }