fix(tasks): speed up resumed task log loading

[tatoalo]

Problem

Opening a task with a long resume chain repeatedly reads the full history for each small response page. This keeps the task view loading much longer as its history grows.

Changes

• Read resume-chain log objects through a process-wide bounded executor while preserving chronological order.
• Read single-run logs directly without executor overhead.
• Increase the bounded session-log response page size to reduce repeated full-history scans.

Benchmark

Local benchmark using a representative multi-run JSONL fixture. The storage benchmark injects 25 ms of latency per object read to compare sequential and bounded-parallel behavior.

Path	Before	After	Speedup
Session-log parsing and pagination	7.99 s	1.17 s	6.8×
Resume-chain storage reads	0.184 s	0.040 s	4.6×
Modeled combined backend path	14.06 s	1.33 s	10.6×

[trunk-io]

😎 Merged manually by @tatoalo - details.

[greptile-apps]

_{Reviews (1): Last reviewed commit: "fix(tasks): bound concurrent log reads" | Re-trigger Greptile}

[stamphog]

Small, contained perf fix within the author's own owning area (bounded thread-pool for parallel log reads, larger page size); no risky territory touched and author has strong familiarity with this code.

• Author wrote 100% of the modified lines and has 31 merged PRs in these paths (familiarity STRONG).
• 👍 on the PR from greptile-apps[bot], hex-security-app[bot].

Gate mechanics and policy version

Gate		Result
prerequisites	✓	all clear
deny-list	✓	no deny categories matched
size	✓	17L, 2F substantive — within ceiling
tier	✓	T1-agent / T1a-trivial (17L, 2F, single-area, fix)
stamphog 2.0.0b3		.stamphog/policy.yml @ a679e1b · reviewed head 959e582

[deployment-status-posthog]

Deploy status

Environment	Status	Deployed At	Workflow
dev	✅ Deployed	2026-07-23 10:44 UTC	Run
prod-us	✅ Deployed	2026-07-23 10:59 UTC	Run
prod-eu	✅ Deployed	2026-07-23 11:03 UTC	Run