diff --git a/internal/setup/plugins/opencode/engram.ts b/internal/setup/plugins/opencode/engram.ts
index c5567087..0e8ea89e 100644
--- a/internal/setup/plugins/opencode/engram.ts
+++ b/internal/setup/plugins/opencode/engram.ts
@@ -89,7 +89,10 @@ Also search memory PROACTIVELY when:
 ### SESSION CLOSE PROTOCOL (mandatory)
 
 Before ending a session or saying "done" / "that's it", you MUST:
-1. Call \`mem_session_summary\` with this structure:
+1. Call \`mem_session_summary\` with the structure below.
+2. Call \`mem_session_end\` with the active session id and an optional summary of work completed.
+
+\`mem_session_summary\` structure:
 
 ## Goal
 [What we were working on this session]
@@ -133,6 +136,9 @@ async function engramFetch(
       headers: opts.body ? { "Content-Type": "application/json" } : undefined,
       body: opts.body ? JSON.stringify(opts.body) : undefined,
     })
+    // Treat non-2xx as failure so callers can avoid false-positive side effects
+    // (e.g. marking a session known when POST /sessions did not succeed).
+    if (!res.ok) return null
     return await res.json()
   } catch {
     // Engram server not running — silently fail
@@ -225,8 +231,7 @@ export const Engram: Plugin = async (ctx) => {
     if (!sessionId || knownSessions.has(sessionId)) return
     // Do not register sub-agent sessions in Engram (issue #116).
     if (subAgentSessions.has(sessionId)) return
-    knownSessions.add(sessionId)
-    await engramFetch("/sessions", {
+    const created = await engramFetch("/sessions", {
       method: "POST",
       body: {
         id: sessionId,
@@ -234,6 +239,10 @@ export const Engram: Plugin = async (ctx) => {
         directory: ctx.directory,
       },
     })
+    // Only mark known after confirmed create so failed requests can retry.
+    if (created != null) {
+      knownSessions.add(sessionId)
+    }
   }
 
   // Try to start engram server if not running
@@ -316,8 +325,24 @@ export const Engram: Plugin = async (ctx) => {
         const info = (event.properties as any)?.info
         const sessionId = info?.id
         if (sessionId) {
+          if (knownSessions.has(sessionId)) {
+            // session.deleted fires once — retry once inline, and only clear
+            // knownSessions after a confirmed /end (do not pretend it closed).
+            let ended = await engramFetch(
+              `/sessions/${encodeURIComponent(sessionId)}/end`,
+              { method: "POST" }
+            )
+            if (ended == null) {
+              ended = await engramFetch(
+                `/sessions/${encodeURIComponent(sessionId)}/end`,
+                { method: "POST" }
+              )
+            }
+            if (ended != null) {
+              knownSessions.delete(sessionId)
+            }
+          }
           toolCounts.delete(sessionId)
-          knownSessions.delete(sessionId)
           subAgentSessions.delete(sessionId)
           lastNudgeTime.delete(sessionId)
         }
diff --git a/internal/setup/setup.go b/internal/setup/setup.go
index 31333c1a..db0fa4a3 100644
--- a/internal/setup/setup.go
+++ b/internal/setup/setup.go
@@ -176,7 +176,10 @@ Also search memory PROACTIVELY when:
 ### SESSION CLOSE PROTOCOL (mandatory)
 
 Before ending a session or saying "done" / "listo" / "that's it", you MUST:
-1. Call mem_session_summary with this structure:
+1. Call mem_session_summary with the structure below.
+2. Call mem_session_end with the active session id and an optional summary of work completed.
+
+mem_session_summary structure:
 
 ## Goal
 [What we were working on this session]
diff --git a/plugin/codex/skills/memory/SKILL.md b/plugin/codex/skills/memory/SKILL.md
index d0ce3f50..ca164f03 100644
--- a/plugin/codex/skills/memory/SKILL.md
+++ b/plugin/codex/skills/memory/SKILL.md
@@ -90,7 +90,10 @@ Also search memory PROACTIVELY when:
 ## SESSION CLOSE PROTOCOL (mandatory)
 
 Before ending a session or saying "done" / "that's it", you MUST:
-1. Call `mem_session_summary` with this structure:
+1. Call `mem_session_summary` with the structure below.
+2. Call `mem_session_end` with the active session id and an optional summary of work completed.
+
+`mem_session_summary` structure:
 
 ## Goal
 [What we were working on this session]
diff --git a/plugin/opencode/engram.ts b/plugin/opencode/engram.ts
index c5567087..0e8ea89e 100644
--- a/plugin/opencode/engram.ts
+++ b/plugin/opencode/engram.ts
@@ -89,7 +89,10 @@ Also search memory PROACTIVELY when:
 ### SESSION CLOSE PROTOCOL (mandatory)
 
 Before ending a session or saying "done" / "that's it", you MUST:
-1. Call \`mem_session_summary\` with this structure:
+1. Call \`mem_session_summary\` with the structure below.
+2. Call \`mem_session_end\` with the active session id and an optional summary of work completed.
+
+\`mem_session_summary\` structure:
 
 ## Goal
 [What we were working on this session]
@@ -133,6 +136,9 @@ async function engramFetch(
       headers: opts.body ? { "Content-Type": "application/json" } : undefined,
       body: opts.body ? JSON.stringify(opts.body) : undefined,
     })
+    // Treat non-2xx as failure so callers can avoid false-positive side effects
+    // (e.g. marking a session known when POST /sessions did not succeed).
+    if (!res.ok) return null
     return await res.json()
   } catch {
     // Engram server not running — silently fail
@@ -225,8 +231,7 @@ export const Engram: Plugin = async (ctx) => {
     if (!sessionId || knownSessions.has(sessionId)) return
     // Do not register sub-agent sessions in Engram (issue #116).
     if (subAgentSessions.has(sessionId)) return
-    knownSessions.add(sessionId)
-    await engramFetch("/sessions", {
+    const created = await engramFetch("/sessions", {
       method: "POST",
       body: {
         id: sessionId,
@@ -234,6 +239,10 @@ export const Engram: Plugin = async (ctx) => {
         directory: ctx.directory,
       },
     })
+    // Only mark known after confirmed create so failed requests can retry.
+    if (created != null) {
+      knownSessions.add(sessionId)
+    }
   }
 
   // Try to start engram server if not running
@@ -316,8 +325,24 @@ export const Engram: Plugin = async (ctx) => {
         const info = (event.properties as any)?.info
         const sessionId = info?.id
         if (sessionId) {
+          if (knownSessions.has(sessionId)) {
+            // session.deleted fires once — retry once inline, and only clear
+            // knownSessions after a confirmed /end (do not pretend it closed).
+            let ended = await engramFetch(
+              `/sessions/${encodeURIComponent(sessionId)}/end`,
+              { method: "POST" }
+            )
+            if (ended == null) {
+              ended = await engramFetch(
+                `/sessions/${encodeURIComponent(sessionId)}/end`,
+                { method: "POST" }
+              )
+            }
+            if (ended != null) {
+              knownSessions.delete(sessionId)
+            }
+          }
           toolCounts.delete(sessionId)
-          knownSessions.delete(sessionId)
           subAgentSessions.delete(sessionId)
           lastNudgeTime.delete(sessionId)
         }