fix(tui): retry transport-class body/decode failures for sub-agent requests

A scout died at 141 seconds because a DeepSeek response stream failed to
decode — the transient classifier's needle list covered headers, timeouts,
resets, and 5xx/429 wording but not body/decode failures, so the child
was classified Fatal on attempt one with zero retries and the parent had
to re-plan from a runtime event (morning-report issue #7).

Body-decode and truncated-response wording now classifies as transient:
'error decoding response body', the Chat API read/parse contexts, and
unexpected-EOF/incomplete-message phrasing. The existing bounded policy
applies unchanged — at most two same-prompt retries with 250ms backoff —
and auth-class failures stay fatal, pinned by the new classifier test.

Verified: subagent suite green; cargo fmt clean.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

crates/tui/src/tools/subagent/mod.rs

@@ -8535,6 +8535,15 @@ fn is_transient_subagent_provider_error(error: &anyhow::Error) -> bool {
         "502",
         "503",
         "504",
+        // Body/decode failures are transport-class: the provider accepted the
+        // request and died mid-response (a DeepSeek stream decode error killed
+        // a 141s scout with zero retries — morning-report issue #7). One
+        // same-prompt retry is cheap next to re-planning the child.
+        "error decoding response body",
+        "failed to read chat api response body",
+        "failed to parse chat api json",
+        "unexpected end of file",
+        "incomplete message",
     ]
     .iter()
     .any(|needle| message.contains(needle))

crates/tui/src/tools/subagent/tests.rs

@@ -5587,6 +5587,27 @@ fn transient_provider_classifier_matches_sse_header_timeout() {
     assert!(is_transient_subagent_provider_error(&err));
 }
 
+#[test]
+fn transient_provider_classifier_matches_body_decode_failures() {
+    // A provider that accepts the request and dies mid-response is a
+    // transport failure, not a fatal child error: one same-prompt retry is
+    // cheap next to re-planning 141 seconds of scout work (morning-report
+    // issue #7, DeepSeek stream decode).
+    let decode = anyhow::anyhow!("error decoding response body")
+        .context("Failed to read Chat API response body");
+    assert!(is_transient_subagent_provider_error(&decode));
+
+    let parse = anyhow::anyhow!("expected value at line 1 column 1")
+        .context("Failed to parse Chat API JSON");
+    assert!(is_transient_subagent_provider_error(&parse));
+
+    let auth = anyhow::anyhow!("401 unauthorized: invalid api key");
+    assert!(
+        !is_transient_subagent_provider_error(&auth),
+        "auth failures stay fatal"
+    );
+}
+
 #[test]
 fn transient_provider_classifier_matches_structured_rate_limit() {
     let err = anyhow::Error::new(crate::llm_client::LlmError::RateLimited {