diff --git a/app/src/ai/blocklist/controller/response_stream.rs b/app/src/ai/blocklist/controller/response_stream.rs
index d28e819b..75921421 100644
--- a/app/src/ai/blocklist/controller/response_stream.rs
+++ b/app/src/ai/blocklist/controller/response_stream.rs
@@ -1059,7 +1059,7 @@ impl ResponseStream {
 
 #[cfg(not(target_family = "wasm"))]
 fn raw_model_request_payload(params: &api::RequestParams, max_chars: usize) -> serde_json::Value {
-    use serde::ser::{SerializeMap, Serializer};
+    use serde::ser::{SerializeMap, SerializeSeq, Serializer};
 
     // collect_str writes debug output directly through serde_json's escaping
     // writer, without format! allocating another copy of potentially large input.
@@ -1070,7 +1070,18 @@ fn raw_model_request_payload(params: &api::RequestParams, max_chars: usize) -> s
         }
     }
 
-    remote_logging::bounded_payload_context(max_chars, |writer| {
+    struct NewestFirst<'a, T>(&'a [T]);
+    impl<T: serde::Serialize> serde::Serialize for NewestFirst<'_, T> {
+        fn serialize<S: Serializer>(&self, serializer: S) -> Result<S::Ok, S::Error> {
+            let mut sequence = serializer.serialize_seq(Some(self.0.len()))?;
+            for message in self.0.iter().rev() {
+                sequence.serialize_element(message)?;
+            }
+            sequence.end()
+        }
+    }
+
+    remote_logging::prefix_bounded_payload_context(max_chars, |writer| {
         let mut serializer = serde_json::Serializer::pretty(writer);
         let mut map = serializer.serialize_map(None)?;
         map.serialize_entry("model_id", &params.model.as_str())?;
@@ -1079,10 +1090,14 @@ fn raw_model_request_payload(params: &api::RequestParams, max_chars: usize) -> s
         map.serialize_entry("computer_use_model_id", &params.computer_use_model.as_str())?;
         map.serialize_entry("input", &DebugPayload(&params.input))?;
         map.serialize_entry("tool_results", &DebugPayload(&params.tool_results))?;
-        map.serialize_entry("tasks", &DebugPayload(&params.tasks))?;
-        map.serialize_entry("message_history", &params.message_history)?;
         map.serialize_entry("progressive_summary", &params.progressive_summary)?;
-        map.serialize_entry("tool_result_archive", &params.tool_result_archive)?;
+        // Preserve the newest request context before old task/debug archives can
+        // consume the diagnostic budget. This ordering affects diagnostics only.
+        map.serialize_entry("message_history_order", "newest_first")?;
+        map.serialize_entry(
+            "message_history",
+            &NewestFirst(params.message_history.as_slice()),
+        )?;
         map.serialize_entry("global_rules", &params.global_rules)?;
         map.serialize_entry("mcp_context", &DebugPayload(&params.mcp_context))?;
         map.serialize_entry("autonomy_level", &DebugPayload(&params.autonomy_level))?;
@@ -1115,7 +1130,9 @@ fn raw_model_request_payload(params: &api::RequestParams, max_chars: usize) -> s
             "omitted_sensitive_fields",
             &["api_keys", "custom_model_providers", "custom_model_routers"],
         )?;
-        map.end()
+        map.serialize_entry("tasks", &DebugPayload(&params.tasks))?;
+        map.serialize_entry("tool_result_archive", &params.tool_result_archive)?;
+        SerializeMap::end(map)
     })
 }
 
diff --git a/app/src/ai/remote_logging.rs b/app/src/ai/remote_logging.rs
index 3adbf129..00bb7929 100644
--- a/app/src/ai/remote_logging.rs
+++ b/app/src/ai/remote_logging.rs
@@ -311,6 +311,89 @@ fn truncate_chars(value: &str, max_chars: usize) -> String {
     truncated
 }
 
+/// Stop serialization once the diagnostic prefix is full. Unlike the tail
+/// collector below, this does not walk the remaining history or tool archive.
+/// A truncated prefix is diagnostic text, not a complete serialized request.
+pub(crate) fn prefix_bounded_payload_context(
+    max_chars: usize,
+    serialize: impl FnOnce(&mut dyn std::io::Write) -> serde_json::Result<()>,
+) -> Value {
+    struct PrefixWriter {
+        bytes: Vec<u8>,
+        max_chars: usize,
+        max_bytes: usize,
+        chars: usize,
+        truncated: bool,
+    }
+
+    impl std::io::Write for PrefixWriter {
+        fn write(&mut self, bytes: &[u8]) -> std::io::Result<usize> {
+            if self.truncated {
+                return Err(std::io::Error::other("diagnostic prefix limit reached"));
+            }
+            let mut included = 0;
+            for byte in bytes {
+                let starts_character = byte & 0xc0 != 0x80;
+                if (starts_character && self.chars == self.max_chars)
+                    || self.bytes.len().saturating_add(included) == self.max_bytes
+                {
+                    self.bytes.extend_from_slice(&bytes[..included]);
+                    self.truncated = true;
+                    return if included == 0 {
+                        Err(std::io::Error::other("diagnostic prefix limit reached"))
+                    } else {
+                        // Respect Write's short-write contract. serde's write_all
+                        // immediately retries the remainder and receives the error.
+                        Ok(included)
+                    };
+                }
+                if starts_character {
+                    self.chars += 1;
+                }
+                included += 1;
+            }
+            self.bytes.extend_from_slice(bytes);
+            Ok(bytes.len())
+        }
+
+        fn flush(&mut self) -> std::io::Result<()> {
+            Ok(())
+        }
+    }
+
+    let mut writer = PrefixWriter {
+        bytes: Vec::new(),
+        max_chars,
+        max_bytes: max_chars.saturating_mul(4),
+        chars: 0,
+        truncated: false,
+    };
+    let result = serialize(&mut writer);
+    if let Err(error) = result {
+        if !writer.truncated {
+            return json!({ "serialization_error": sanitize_error(error) });
+        }
+    }
+    // Writers may split a UTF-8 character across calls. Keep only a complete
+    // prefix if serialization stopped before the last character was finished.
+    let valid_length = match std::str::from_utf8(&writer.bytes) {
+        Ok(_) => writer.bytes.len(),
+        Err(error) => error.valid_up_to(),
+    };
+    writer.bytes.truncate(valid_length);
+    let payload = String::from_utf8(writer.bytes).expect("validated diagnostic UTF-8 prefix");
+    let included_chars = payload.chars().count();
+    json!({
+        "payload": payload,
+        "payload_total_chars": if writer.truncated { None } else { Some(included_chars) },
+        "payload_included_chars": included_chars,
+        "payload_max_chars": max_chars,
+        "truncated": writer.truncated,
+        "truncation_strategy": if writer.truncated { Some("prefix") } else { None },
+        "serialization_stopped_early": writer.truncated,
+    })
+}
+
 /// Serialize directly into a bounded UTF-8 tail instead of materializing the full
 /// request and its archive as a JSON Value and then another large String.
 pub(crate) fn bounded_payload_context(
diff --git a/app/src/ai/remote_logging_tests.rs b/app/src/ai/remote_logging_tests.rs
index d697e37b..f1691dde 100644
--- a/app/src/ai/remote_logging_tests.rs
+++ b/app/src/ai/remote_logging_tests.rs
@@ -64,3 +64,79 @@ fn streamed_json_matches_serialized_payload_without_materializing_the_archive()
     });
     assert_eq!(actual, tail_limited_payload_context(&expected, 100));
 }
+
+#[test]
+fn prefix_payload_preserves_utf8_and_reports_unknown_truncated_size() {
+    let payload = "é日本🙂 ending";
+    for limit in [0, 1, 3, 4, payload.chars().count(), payload.len()] {
+        for chunk_size in [1, 2, 7, payload.len()] {
+            let actual = super::prefix_bounded_payload_context(limit, |writer| {
+                for chunk in payload.as_bytes().chunks(chunk_size) {
+                    writer.write_all(chunk).map_err(serde_json::Error::io)?;
+                }
+                Ok(())
+            });
+            let expected = payload.chars().take(limit).collect::<String>();
+            let truncated = limit < payload.chars().count();
+            assert_eq!(actual["payload"], expected);
+            assert_eq!(actual["payload_included_chars"], expected.chars().count());
+            assert_eq!(actual["truncated"], truncated);
+            assert_eq!(actual["serialization_stopped_early"], truncated);
+            assert_eq!(
+                actual["payload_total_chars"],
+                if truncated {
+                    serde_json::Value::Null
+                } else {
+                    json!(payload.chars().count())
+                }
+            );
+        }
+    }
+}
+
+#[test]
+fn prefix_payload_stops_pretty_debug_serialization_at_the_budget() {
+    use std::cell::Cell;
+
+    struct LargeDebug<'a>(&'a Cell<usize>);
+    impl std::fmt::Debug for LargeDebug<'_> {
+        fn fmt(&self, formatter: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+            for _ in 0..1_000_000 {
+                self.0.set(self.0.get() + 1);
+                formatter.write_str("large archive entry ")?;
+            }
+            Ok(())
+        }
+    }
+    struct DebugPayload<'a>(LargeDebug<'a>);
+    impl serde::Serialize for DebugPayload<'_> {
+        fn serialize<S: serde::Serializer>(&self, serializer: S) -> Result<S::Ok, S::Error> {
+            serializer.collect_str(&format_args!("{:#?}", self.0))
+        }
+    }
+
+    let visited = Cell::new(0);
+    let actual = super::prefix_bounded_payload_context(64, |writer| {
+        serde_json::to_writer(writer, &DebugPayload(LargeDebug(&visited)))
+    });
+
+    assert!(visited.get() < 10);
+    assert_eq!(actual["payload_included_chars"], 64);
+    assert_eq!(actual["truncated"], true);
+    assert_eq!(actual["payload_total_chars"], serde_json::Value::Null);
+    assert_eq!(actual["truncation_strategy"], "prefix");
+}
+
+#[test]
+fn prefix_payload_keeps_real_serialization_errors_visible() {
+    let actual = super::prefix_bounded_payload_context(100, |_writer| {
+        Err(serde_json::Error::io(std::io::Error::other(
+            "test serializer failed",
+        )))
+    });
+    assert!(actual["serialization_error"]
+        .as_str()
+        .unwrap()
+        .contains("test serializer failed"));
+    assert!(actual.get("payload").is_none());
+}
diff --git a/app/src/ai/runtime/rig_request.rs b/app/src/ai/runtime/rig_request.rs
index e0b224cd..53417c3c 100644
--- a/app/src/ai/runtime/rig_request.rs
+++ b/app/src/ai/runtime/rig_request.rs
@@ -844,6 +844,11 @@ fn provider_safe_mcp_tool_name(server_id: Option<&str>, tool_name: &str) -> Stri
     format!("{prefix}{component}{separator}{hash}")
 }
 
+fn deduplicate_context_entries<T: Clone + Eq + std::hash::Hash>(entries: &mut Vec<T>) {
+    let mut seen = HashSet::with_capacity(entries.len());
+    entries.retain(|entry| seen.insert(entry.clone()));
+}
+
 fn build_system_prompt(
     inputs: &[AIAgentInput],
     tools: &[ToolDefinition],
@@ -988,6 +993,13 @@ fn build_system_prompt(
             AIAgentContext::Image(_) => {}
         }
     }
+    // Grouped inputs, such as background-job completions, can share the same context.
+    // Emit each exact context entry once, retaining its first position and all distinct
+    // content. Conversational inputs and tool results remain separate and unchanged.
+    deduplicate_context_entries(&mut environment);
+    deduplicate_context_entries(&mut project_rules);
+    deduplicate_context_entries(&mut attached_context);
+    deduplicate_context_entries(&mut available_skills);
     if !environment.is_empty() {
         prompt.push_str("## Environment\n");
         for item in environment {
diff --git a/app/src/ai/runtime/rig_request_tests.rs b/app/src/ai/runtime/rig_request_tests.rs
index f2088ea3..a4be9f9f 100644
--- a/app/src/ai/runtime/rig_request_tests.rs
+++ b/app/src/ai/runtime/rig_request_tests.rs
@@ -81,6 +81,177 @@ fn native_context_reaches_rig_without_a_proto_context_conversion() {
     assert!(prompt.contains("Indexed codebase: galaxy (/repo)"));
 }
 
+fn shared_prompt_context(
+    directory: &str,
+    rule: &str,
+    attachment: &str,
+    skill_description: &str,
+) -> Vec<AIAgentContext> {
+    vec![
+        AIAgentContext::Directory {
+            pwd: Some(directory.to_string()),
+            home_dir: Some("/home/user".to_string()),
+            are_file_symbols_indexed: false,
+        },
+        AIAgentContext::ProjectRules {
+            root_path: "/repo".to_string(),
+            active_rules: vec![FileContext::new(
+                "/repo/AGENTS.md".to_string(),
+                AnyFileContent::StringContent(rule.to_string()),
+                None,
+                None,
+            )],
+            additional_rule_paths: Vec::new(),
+        },
+        AIAgentContext::File(FileContext::new(
+            "/repo/context.txt".to_string(),
+            AnyFileContent::StringContent(attachment.to_string()),
+            None,
+            None,
+        )),
+        AIAgentContext::Skills {
+            skills: vec![SkillDescriptor {
+                reference: SkillReference::Path(LocalOrRemotePath::Local(PathBuf::from(
+                    "/repo/.agents/skills/context-probe/SKILL.md",
+                ))),
+                name: "context-probe".to_string(),
+                description: skill_description.to_string(),
+                scope: SkillScope::Project,
+                provider: SkillProvider::Agents,
+                icon_override: None,
+            }],
+        },
+    ]
+}
+
+#[test]
+fn grouped_completions_share_context_without_dropping_inputs_or_tool_results() {
+    let context = shared_prompt_context(
+        "/repo",
+        "shared-rule-probe",
+        "shared-attachment-probe",
+        "shared-skill-description-probe",
+    );
+    let mut params = RequestParams::new_for_test();
+    params.input = (0..4)
+        .map(|index| AIAgentInput::CommandCompletionAssessment {
+            prompt: format!("Completion evidence for job {index}"),
+            context: Arc::from(context.clone()),
+            completed_command: crate::ai::agent::RunningCommand {
+                command: format!("command-{index}"),
+                block_id: format!("background-job:{index}").into(),
+                grid_contents: String::new(),
+                cursor: String::new(),
+                requested_command_id: None,
+                is_alt_screen_active: false,
+            },
+        })
+        .collect();
+    // Repeated user restrictions remain distinct conversational inputs.
+    params.input.extend([
+        user_query_with_context("Do not deploy", context.clone()),
+        user_query_with_context("Do not deploy", context),
+    ]);
+    params.message_history = vec![galaxy_agent_core::ConversationMessage {
+        role: MessageRole::Assistant,
+        content: MessageContent::ToolUse {
+            tool_use_id: "retained-call".to_string(),
+            name: "read_files".to_string(),
+            input: serde_json::json!({ "files": ["/repo/file.rs"] }),
+        },
+    }];
+    params.tool_results = vec![ToolResult {
+        call_id: "retained-call".to_string(),
+        content: "retained-tool-result-probe".to_string(),
+        status: ToolResultStatus::Success,
+        images: Vec::new(),
+    }];
+
+    let prepared = prepare_rig_turn(
+        &config(),
+        params,
+        vec![ToolType::ReadFiles, ToolType::ReadSkill],
+        Vec::new(),
+    );
+    let prompt = prepared.request.system_prompt.expect("system prompt");
+    for entry in [
+        "Working directory: /repo",
+        "Home directory: /home/user",
+        "shared-rule-probe",
+        "shared-attachment-probe",
+        "shared-skill-description-probe",
+    ] {
+        assert_eq!(
+            prompt.matches(entry).count(),
+            1,
+            "repeated context: {entry}"
+        );
+    }
+    for index in 0..4 {
+        assert!(prepared.request.messages.iter().any(|message| {
+            matches!(&message.content, MessageContent::Text(text)
+                if text == &format!("Completion evidence for job {index}"))
+        }));
+    }
+    assert_eq!(
+        prepared
+            .request
+            .messages
+            .iter()
+            .filter(|message| {
+                matches!(&message.content, MessageContent::Text(text) if text == "Do not deploy")
+            })
+            .count(),
+        2,
+    );
+    assert!(prepared.request.messages.iter().any(|message| {
+        matches!(&message.content, MessageContent::ToolResult { tool_use_id, content, .. }
+            if tool_use_id == "retained-call" && content == "retained-tool-result-probe")
+    }));
+}
+
+#[test]
+fn distinct_context_content_keeps_its_first_order_even_with_shared_paths() {
+    let first = shared_prompt_context(
+        "/repo/first",
+        "first-rule-probe",
+        "first-attachment-probe",
+        "first-skill-description-probe",
+    );
+    let second = shared_prompt_context(
+        "/repo/second",
+        "second-rule-probe",
+        "second-attachment-probe",
+        "second-skill-description-probe",
+    );
+    let mut params = RequestParams::new_for_test();
+    params.input = vec![
+        user_query_with_context("First instruction", first.clone()),
+        user_query_with_context("Second instruction", second),
+        user_query_with_context("Third instruction", first),
+    ];
+
+    let prepared = prepare_rig_turn(&config(), params, vec![ToolType::ReadSkill], Vec::new());
+    let prompt = prepared.request.system_prompt.expect("system prompt");
+    for (first, second) in [
+        (
+            "Working directory: /repo/first",
+            "Working directory: /repo/second",
+        ),
+        ("first-rule-probe", "second-rule-probe"),
+        ("first-attachment-probe", "second-attachment-probe"),
+        (
+            "first-skill-description-probe",
+            "second-skill-description-probe",
+        ),
+    ] {
+        assert_eq!(prompt.matches(first).count(), 1);
+        assert_eq!(prompt.matches(second).count(), 1);
+        assert!(prompt.find(first).unwrap() < prompt.find(second).unwrap());
+    }
+    assert_eq!(prepared.request.messages.len(), 3);
+}
+
 #[test]
 fn volatile_request_time_follows_the_cacheable_system_prompt_prefix() {
     let mut params = RequestParams::new_for_test();