feat(orchestrator): add Background Job Board guidance to base prompt

[stevekstevek]

What changed

Added a ### Background Job Board section to buildOrchestratorPrompt() and a session-reuse warning to ### Session Reuse.

Why

Testing after the [just launched]/[resumed] label patch (#486) revealed two additional failure modes:

1. Autoregressive ID regeneration
The model rewrites long session IDs from memory when recalling them for subsequent task_status calls, introducing character-level errors (e.g., Ob → Ab). The model's own explanation of the typo was wrong — it didn't understand what it had done. Fix: instruct the model to use short aliases (lib-1) for reasoning and copy full IDs verbatim from tool outputs only when tools require them.

2. Dual-context confusion
The Resumable Sessions context section shows the same session IDs as the job board but without temporal labels. When a model sees the same ID in two places — one with [just launched], one without a timestamp — it resolves the contradiction by treating the task as pre-existing. The prompt now explicitly explains that these two sections serve different purposes.

3. Session reuse requires explicit action
Testing showed the model intending to reuse sessions but dispatching fresh ones because it didn't pass task_id. Added explicit rule: intent alone doesn't reuse a session.

Relationship to #486

This prompt section references the [just launched] and [resumed] labels introduced in #486. The two changes are complementary: the code creates the signal; the prompt teaches the model how to interpret it.

[greptile-apps]

Greptile Summary

This PR extends buildOrchestratorPrompt() with two additions: a session-reuse rule clarifying that task_id must be explicitly passed to avoid creating a fresh session, and a new ### Background Job Board section teaching the model how to interpret alias-based task tracking and the [just launched]/[resumed] labels introduced in #486.

• The session-reuse rule is a clear, correct addition that closes the intent-vs-execution gap documented in the PR description.
• The new ### Background Job Board section uses the same markdown heading as the one dynamically emitted by BackgroundJobBoard.formatForPrompt(), which is injected into every orchestrator user-message turn at runtime — resulting in two same-named sections visible simultaneously, with subtly different instructions.
• The status-line legend covers completed, unreconciled but omits error, unreconciled, cancelled, unreconciled, and <state>, timed out, all of which are valid outputs from formatJob().

Confidence Score: 3/5

The change is prompt-only and carries no risk of data loss or runtime crashes, but the duplicate heading creates a real coherence problem when active background jobs are present.

The session-reuse line is safe and correct. The new Background Job Board section, however, shares an identical heading with the live job data injected into every orchestrator user-message turn, so at runtime the model sees two ### Background Job Board headings with different (and somewhat conflicting) instructions. This is a present, reproducible issue on any turn with active background jobs. The legend is also incomplete for error and timed-out statuses the job board regularly produces.

src/agents/orchestrator.ts — the new static section and how it interacts with the dynamic injection in src/hooks/task-session-manager/index.ts:585 and src/utils/background-job-board.ts:194.

Important Files Changed

Filename	Overview
src/agents/orchestrator.ts	Adds static ### Background Job Board guidance and a session-reuse rule to the orchestrator system prompt. The guidance content is accurate but the section heading duplicates the one emitted by BackgroundJobBoard.formatForPrompt(), which the runtime injects into every orchestrator user-message turn — creating two same-named sections with conflicting instructions visible simultaneously.

_{Reviews (1): Last reviewed commit: "feat(orchestrator): add Background Job B..." | Re-trigger Greptile}

[greptile-apps]

Duplicate heading collides with dynamic job board injection

BackgroundJobBoard.formatForPrompt() already emits its own ### Background Job Board heading (with live job rows) and injects it into every orchestrator user-message turn via task-session-manager/index.ts:585. When active jobs exist the model therefore sees two distinct ### Background Job Board sections — one in the system prompt (instructions, no data) and one in the injected user-message context (abbreviated instruction + actual job rows). Because the headings are identical, the model may conflate them and either look for live job data inside the system-prompt section (finding none) or treat the two differing instructions ("Use the alias in your reasoning" vs. "Use task_status before consuming running jobs") as contradictory directives scoped to the same section. Renaming the static section — e.g. ### Background Job Board — Usage Guide — would disambiguate.

[greptile-apps]

Incomplete status-line coverage leaves timed-out and non-completed terminal states unexplained

BackgroundJobBoard.formatJob() emits three distinct status patterns: ${state}, unreconciled for any terminal-unreconciled job (so error, unreconciled and cancelled, unreconciled are equally possible), ${state}, timed out when timedOut is set (e.g. running, timed out), and the plain running / running [label] entries. The guidance here only documents completed, unreconciled, so the model has no instruction for how to treat error, unreconciled, cancelled, unreconciled, or running, timed out entries it will routinely encounter.