feat(session): support multiple PRs per session

[Pritom14]

Summary

Lets a single session own several pull requests (a root plus stacked children) instead of being capped at one. The SQLite schema was already 1-session→many-PR (pr.url PK, session_id a plain FK with idx_pr_session, no UNIQUE on session_id), so this is a behavioural change across the observe → persist → derive → react pipeline, not a migration.

State & user-action flow

The session's display status is never stored — it is derived at read time from durable PR facts. One full loop:

1. Agent opens PR(s). A root PR on the session branch (feat/x), optionally stacked children on the feat/x/... convention.
2. OBSERVE (observe/scm): each poll lists the repo's open PRs, attributes every PR whose source branch equals the session branch or descends from it to the owning session (longest-prefix wins), and persists the pr row including the source/target branch pair.
3. DERIVE (service/session/status.go, read-time): session status = worst-wins aggregate over the open PRs, by severity ci_failed > changes_requested > draft > review_pending > pr_open > approved > mergeable. A stacked child whose parent is still open is excluded from the aggregate (it cannot merge until the parent does). The stack model + per-PR facts are surfaced as prs[] on every session DTO, so the dashboard shows each PR's state.
4. ACT (lifecycle/reactions.go): per-PR nudges to the agent — CI failing → "fix CI" (with log tail); review changes/unresolved comments → "address feedback"; merge conflict → "rebase", but only the bottom of the stack; a stacked child blocked by an open parent is suppressed. Dedup signature is persisted per PR so a daemon restart never re-fires.
5. User action closes the loop. From the derived status + prs[] the user/agent fixes CI, addresses review, or rebases and pushes; the next poll re-observes and re-derives. No status is ever written back — only PR facts are.
6. Completion. The session terminates (→ status merged) only when no PR is open and at least one merged. A single PR merging while another stays open keeps the session alive.

What changed, by layer

• Observe (observe/scm/observer.go): one refresh subject per open tracked PR; discoverNewPRs + matchSession do the branch-prefix attribution (longest match wins so a child session claims its own stacked PRs).
• Derive (service/session/stack.go, status.go): worst-wins aggregation + stack model (B is a child of A iff B.target_branch == A.source_branch and A is open), surfaced as prs[].
• React (lifecycle/reactions.go): per-PR reactions, stacked-child nudge suppression, and sessionComplete (all closed/merged + ≥1 merged).
• API (httpd/controllers/dto.go, sessions.go, regenerated openapi.yaml + frontend/src/api/schema.ts): prs[] on the session views via SessionView.

Tests

• Unit coverage across stack, status, observer multi-subject discovery, and lifecycle per-PR reactions/completion.
• A real-SQLite store test (store/pr_facts_test.go) for the stacked-PR read path: ListPRFactsForSession returns every owned PR newest-first with state flags and branch pair preserved (the data the stack aggregator builds on).
• Functional end-to-end (integration/scm_observer_test.go, TestSCMObserverMultiPREndToEnd) drives the real sqlite.Store + lifecycle.Manager + observe/scm.Observer (canned provider only) through: (1) one session owning its root and stacked child from a single repo list with branch pairs persisted; (2) staying alive while a stacked PR is open and terminating only once all merge; (3) a stacked child blocked by an open parent suppressed while the stack bottom is nudged (asserted down to the persisted dedup signature).

Test plan

• go build ./... clean
• go vet ./... clean
• go test ./... green (53 packages, exit 0)
• TestSCMObserverMultiPREndToEnd passes (attribution / completion / nudge suppression)
• Live agent-driven run: spawning an agent that opens multiple real GitHub PRs on one session. Needs a real GitHub repo + agent credentials/environment not available in this workspace, so it is not exercised here — the functional proof above drives the real store/lifecycle/observer against a canned SCM provider instead.

🤖 Generated with Claude Code

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[illegalcall]

Two correctness issues to address before merging:

1. backend/internal/lifecycle/reactions.go: session completion should account for PRs discovered in the same poll before terminating. If a terminal PR observation is processed before a newly discovered sibling/child is persisted, the session can terminate while an open PR from that same poll is still pending.

2. backend/internal/adapters/scm/github/observer_provider.go: branch-prefix attribution should ignore forked PR heads. head.ref alone can misattribute a fork PR whose branch name matches an AO session branch; carry/filter by head repo owner/full name so only PRs from the project repo are auto-claimed.

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[Pritom14]

Two correctness issues to address before merging:

1. backend/internal/lifecycle/reactions.go: session completion should account for PRs discovered in the same poll before terminating. If a terminal PR observation is processed before a newly discovered sibling/child is persisted, the session can terminate while an open PR from that same poll is still pending.
2. backend/internal/adapters/scm/github/observer_provider.go: branch-prefix attribution should ignore forked PR heads. head.ref alone can misattribute a fork PR whose branch name matches an AO session branch; carry/filter by head repo owner/full name so only PRs from the project repo are auto-claimed.

addressed

[illegalcall]

Two remaining review notes:

1. backend/internal/service/session/status.go: stack-blocked child PRs are excluded from status aggregation entirely. That hides actionable child signals like failing CI, draft state, requested changes, or unresolved comments. The stack exemption should only suppress mergeability/conflict readiness for blocked children, not CI/review/draft signals.

2. backend/internal/session_manager/manager.go: the worker prompt says independent PRs can “branch off your base branch as usual,” but auto-attribution only matches the session branch or session-branch/... descendants. Please clarify that independent PRs may target the base branch, but their source branches still need to stay under the session namespace.

The previous same-poll completion and fork-attribution issues look fixed in the latest commit.

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[Pritom14]

Two remaining review notes:

1. backend/internal/service/session/status.go: stack-blocked child PRs are excluded from status aggregation entirely. That hides actionable child signals like failing CI, draft state, requested changes, or unresolved comments. The stack exemption should only suppress mergeability/conflict readiness for blocked children, not CI/review/draft signals.
2. backend/internal/session_manager/manager.go: the worker prompt says independent PRs can “branch off your base branch as usual,” but auto-attribution only matches the session branch or session-branch/... descendants. Please clarify that independent PRs may target the base branch, but their source branches still need to stay under the session namespace.

The previous same-poll completion and fork-attribution issues look fixed in the latest commit.

addressed