fix(server): shed only retryable object-journal reads under load (#19176)

Client polling can exhaust the shared object journal queue and reject log persistence. Bound ordinary object-log and trace reads, keep persistence and internal verification queued, and return retryable 503 responses when reads are busy. Leave feedback exports unsent until every log page is available.

Validation: 72 latest-master affected tests and 10 workflow tests pass locally, with the workflow fixture passing strict TypeScript checks. The preceding broader run passed 280 server tests with two opt-in S3 skips. All applicable checks on d0a937768d are green (56 success, three skipped); exact-head Apex review is 5/5 with no unresolved findings. Background persistence still has no fixed queue bound during a prolonged storage outage.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Co-Authored-By: Paperclip <noreply@paperclip.ing>

tests/runner-e2e/workflow-target.test.ts

@@ -18,8 +18,7 @@ async function resolveTarget(event: string, cadence: string, branch = "master")
       encoding: "utf8", env: { ...process.env, EVENT_NAME: event, EVAL_CADENCE: cadence,
         IMAGE_ONLY: "false", TESTOPS_REQUESTED: "false",
         TARGET_BRANCH: branch, DEFAULT_BRANCH: "master", GITHUB_SHA: queuedSha,
-        MOCK_BRANCH_SHA: advancedSha, GITHUB_OUTPUT: output, REPOSITORY: "paperclipai/paperclip",
-        IMAGE_ONLY: "false", TESTOPS_REQUESTED: "false" },
+        MOCK_BRANCH_SHA: advancedSha, GITHUB_OUTPUT: output, REPOSITORY: "paperclipai/paperclip" },
     });
     return { status: result.status, stderr: result.stderr,
       output: await readFile(output, "utf8").catch(() => "") };