PR conflict simulation

ADE predicts PR merge conflicts before the user hits Merge by running git merge-tree locally. This covers three PR-adjacent scenarios:

1. PR-to-base — will this PR land cleanly on its base branch?
2. Pairwise integration — do any two source PRs in an integration proposal conflict with each other?
3. Lane rebase — is the lane behind its parent or base branch, and if so, does rebasing produce conflicts?

All three use the shared conflict service primitives documented in ../conflicts/README.md and ../conflicts/detection.md. This doc focuses on the PR-surface specifics.

PR-to-base simulation

conflictService.simulateMerge({ laneAId }) (omit laneBId for lane-to-base) runs:

git merge-tree <base> <lane-HEAD>

Results:

• outcome: "clean" — no conflicts.
• outcome: "conflict" — a list of conflicting files with marker previews.
• outcome: "error" — the merge-tree command failed (typically a bad ref or corrupt index).

The PR detail pane surfaces the outcome in the merge readiness panel. When outcome is conflict, the "Merge" button is disabled unless the user opts into merge bypass (and only when the PR is not locally conflicting).

Pairwise integration simulation

prService.simulateIntegration({ sourceLaneIds, baseBranch, mergeIntoLaneId? }) runs the pairwise matrix for an integration (merge-plan) proposal:

1. buildIntegrationPreflight validates:
   • at least one source lane
   • no duplicate source lane ids (duplicateSourceLaneIds)
   • no missing source lane ids (missingSourceLaneIds)
2. Resolve baseSha via git rev-parse <baseBranch>.
3. For each source lane, read headSha, commitCount, and diffStat against the base.
4. For each unordered pair (i, j) with i < j:
   • runGitMergeTree({ mergeBase: baseSha, branchA: headSha_i, branchB: headSha_j, timeoutMs: 30_000 }).
   • Exit code 128 is a fatal git error — both lanes are marked as blocked.
   • Non-zero exit without conflicts is also treated as blocked (an unknown state).
   • Otherwise: parse conflict tree OID, list conflicting files, produce marker previews via parseConflictMarkers.
5. Compute per-lane summary rows (laneSummaries) with position, commit hash, commit count, and diff stat.
6. If mergeIntoLaneId is present, resolve that lane's HEAD and run additional merge-tree checks from the adopted merge target against each source lane. This does not replace the child-vs-child pairwise matrix; it adds target-lane conflict evidence.
7. Return IntegrationProposal with pairwise results, lane summaries, computed overall outcome, and optional merge-target metadata.

IntegrationProposal fields include:

• steps — serialized merge plan with per-step status.
• pairwiseResults — Array<{ laneAId, laneBId, outcome: "clean" | "conflict" | "blocked", conflictingFiles }>.
• laneSummaries — per-lane commit hash, position, conflictsWith[].
• overallOutcome — "clean" | "conflict" | "blocked".
• preferredIntegrationLaneId — selected existing merge target lane when the proposal should merge into an adopted lane.
• mergeIntoHeadSha — selected merge target HEAD at simulation time, used to detect drift before commit.

Conflict marker parsing

Conflict previews come from parseConflictMarkers in prService.ts:

const markerRegex = /(<<<<<<<[^\r\n]*\r?\n)([\s\S]*?)(=======\r?\n)([\s\S]*?)(>>>>>>>[^\r\n]*)/g;

Handles \r\n line endings alongside \n for Windows compatibility. Extracts:

• conflictMarkers — the raw marker blocks joined with --- separators, capped at 2000 bytes.
• oursExcerpt / theirsExcerpt — the content between markers, each capped at 500 bytes.
• diffHunk — the first 12 lines of each marker block joined.

The parser is shared between readConflictFilePreviewFromWorktree and the integration merge flow so they produce identical output.

hasMergeConflictMarkers(content) in integrationValidation.ts is the gating check used before parsing. It requires all three markers (<<<<<<<, =======, >>>>>>>) to be present.

Integration lane creation

When a proposal's plan is accepted, ADE either creates a dedicated integration lane or adopts an existing lane as the merge target.

createIntegrationLaneForProposal:

1. Ensure the proposal has no integration_lane_id yet.
2. If preferred_integration_lane_id is set, validate that lane still exists, is not a source lane, is not primary, and passes the dirty worktree preflight unless allowDirtyWorktree was explicitly set.
3. Otherwise create a child lane under the base branch, name integration-<short-id>.
4. Persist integration_lane_id on the proposal row. The display origin is inferred as adopted when the preferred lane became the integration lane; otherwise it is ade-created.
5. Emit lane/PR events so graph and workflow surfaces refresh.

commitIntegration runs the actual merges sequentially:

1. For each step in stack-depth order, merge the source lane's head into the integration lane.
2. Pause on conflict — the user can run the external resolver (Codex / Claude) through the Integration tab.
3. On success, mark the step committed.
4. When all steps complete, flip the proposal's workflow_display_state to history and surface cleanup actions.

cleanupIntegrationWorkflow prompts the user to declare whether to delete the integration lane / its source lanes / neither, and records the decision in cleanup_state. Adopted merge-target lanes are kept by default because ADE did not create them for the proposal.

Rebase prediction

The same merge-tree primitive powers rebase prediction. For each lane, scanRebaseNeeds computes:

• behindBy — commit count difference against the comparison ref.
• conflictPredicted — true if git merge-tree reports conflicts.
• conflictingFiles — when conflictPredicted, the paths that would conflict on rebase.

The comparison ref is resolved via resolveLaneRebaseTarget:

• Parent lane branch (if non-primary parent and shouldLaneTrackParent)
• origin/<baseRef> with fallback to local <baseRef>

This keeps the PR Rebase tab's prediction consistent with the lane service's actual rebase target (they use the same resolver).

Caching and staleness

Prediction results are stored in the conflict_predictions table:

Column	Use
lane_a_id, lane_b_id	pair (or lane-to-base when lane_b_id IS NULL)
status	clean / conflict / unknown
conflicting_files_json	JSON array of { path, conflictType }
overlap_files_json	paths touched on both sides
lane_a_sha, lane_b_sha	head SHAs at prediction time
predicted_at	ISO timestamp
expires_at	when the prediction goes stale

STALE_MS = 5 * 60_000 — predictions older than 5 minutes are marked stale and surfaced with a clock indicator in the UI.

The prediction engine runs:

• Periodically via the job engine (background sweep).
• On-demand via ade.conflicts.runPrediction (user-triggered from the UI).
• Realtime when a lane's dirty state changes and overlap is detected with a peer lane.

IPC surface (PR side)

PR-specific IPC that consumes the conflict/simulation stack:

Channel	Description
ade.prs.simulateIntegration	Compute pairwise integration matrix
ade.prs.createIntegrationLaneForProposal	Create or adopt merge-target lane
ade.prs.commitIntegration	Sequentially merge source lanes into the integration lane
ade.prs.cleanupIntegrationWorkflow	Record cleanup decision
ade.prs.getMergeContext	Read PR merge readiness (mergeable, behind-by, conflicts)
ade.prs.recheckIntegrationStep	Re-simulate a single integration step

Shared conflict IPC consumed by PR flows:

Channel	Description
ade.conflicts.simulateMerge	Run a merge simulation between two lanes (or lane-to-base)
ade.conflicts.getLaneStatus	Lane conflict status badge
ade.conflicts.listOverlaps	Per-peer overlap lists
ade.conflicts.runPrediction	Trigger prediction for a lane or pair
ade.conflicts.getBatchAssessment	Batch view (used by Graph risk matrix)

Renderer wiring

• PrDetailPane.tsx reads merge context on PR select and renders mergeability + conflict badges.
• IntegrationTab.tsx (3022 lines) is the primary consumer for pairwise simulation. It builds the matrix, streams per-step commits, and surfaces blocked/conflict states with resolver entry points.
• ConflictFilePreview.tsx renders file-level conflict markers from the parsed output.
• IntegrationPrContextPanel.tsx shows the integration proposal's evidence inline on the PR detail.
• graph/shared/RiskMatrix.tsx renders the full pairwise matrix (see ../workspace-graph/README.md).

Gotchas

• git merge-tree exit codes. Exit 0 = clean or conflict (parse stdout to differentiate). Exit 128 = fatal (corrupt ref, missing object). Any other non-zero with no conflicts = unknown state; both lanes are marked blocked rather than assumed clean. Blocking blocks surface in the integration UI with a log warning.
• Commit count vs diff stat path. rev-list --count <base>..<head> counts commits; diff --shortstat reports aggregate insertions/deletions. When headSha is null (rev-parse failed), the lane summary carries commitCount: 0 and diffStat: 0/0/0.
• Base SHA is resolved once per proposal simulation. All lanes compare against the same baseSha so pairwise results are internally consistent even if the base branch advances mid-run.
• The \0 sanitization in the merge-tree unknown log preserves stdout for debugging without letting null bytes break the structured log. If you change this, test with a real merge-tree tree OID that contains NULs.
• Marker parser caps are not user-configurable. 2000/500/500 byte caps are hardcoded for predictable prompt sizes downstream.
• conflictType is always "content" from the parser. Rename / delete / add conflicts are detected at the git level, not via the marker parser.