Greptile Summary

This PR fixes a long-standing bug in subagent duration display where runtimes were shown as ~5–6× inflated (e.g., "1m" for a 5-second task). The root cause was a duplicate formatDurationCompact in src/shared/subagents-format.ts that divided milliseconds directly by 60,000 — skipping the ms→s conversion entirely — and also enforced a minimum of 1 minute via Math.max(1, ...).

The fix replaces the buggy local duplicate with a re-export of the canonical formatDurationCompact from src/infra/format-time/format-duration.ts, which correctly handles the full ms → s → m → h → d decomposition and provides seconds-level granularity. The two call sites in subagent-control.ts and commands-subagents/shared.ts are updated to add ?? "n/a" to preserve the original fallback display for invalid/zero inputs (the canonical function returns undefined rather than "n/a"). A third call site (action-info.ts) already had this fallback and required no change.

Key changes:

• src/shared/subagents-format.ts: local formatDurationCompact replaced with re-export of canonical implementation
• src/agents/subagent-control.ts & src/auto-reply/reply/commands-subagents/shared.ts: ?? "n/a" fallback added to match prior behavior for invalid inputs
• src/shared/subagents-format.test.ts: regression tests added covering seconds, minutes, hours, and invalid-input cases

Confidence Score: 5/5

• This PR is safe to merge — it is a targeted, well-tested bug fix with no risk of regressions.
• The change is minimal and surgical: it removes a demonstrably broken local function (wrong divisor of 60,000) and replaces it with a re-export of the canonical, already-tested implementation. All three call sites that depend on a non-undefined return value have ?? "n/a" fallbacks. The new regression tests correctly verify seconds-level output as well as boundary behaviour for minutes, hours, and invalid inputs. No new logic is introduced.
• No files require special attention.

_{Last reviewed commit: 1bee70d}

Closing to free up PR queue — will resubmit if needed.