diff --git a/README.md b/README.md
index 76f7a953d9..faab923398 100644
--- a/README.md
+++ b/README.md
@@ -102,7 +102,7 @@ Human gate        Human gate                              Human merge
 
 1. **Refine**: Agents analyze the task, research the codebase, produce requirements. Reviewers validate. Human approves before planning.
 2. **Plan**: Architect recommends approach, task planner breaks it into discrete tasks with acceptance criteria, risk analyst flags concerns. Human approves before any code is written.
-3. **Implement**: Coder writes code, tester writes tests and runs linters/type-checkers, documenter updates docs. Code and contract reviewers provide line-level feedback; security and concurrency lens reviewers add targeted cross-file analysis and block consensus on a NACK. Cycles continue until all checks pass and BRC consensus is reached.
+3. **Implement**: The plan's tasks are split into a **DAG of independent slices** — each slice runs as its own agent team on its own integration branch with its own BRC consensus and stacked PR. Slices whose dependencies are satisfied run concurrently (up to `EGG_ORCH_MAX_PARALLEL_SLICES`, default 5); slices with unmet dependencies wait in subsequent waves. Within each slice, the coder writes code, the tester writes tests and runs linters/type-checkers, and the documenter updates docs. Code and contract reviewers provide line-level feedback; security and concurrency lens reviewers add targeted cross-file analysis and block consensus on a NACK. Cycles continue until all checks pass and BRC consensus is reached for that slice. See [Slice-DAG Implement Phase](docs/architecture/slice-dag.md) for the full model.
 4. **PR**: Orchestrator auto-creates the PR from plan metadata. Only a human can merge via GitHub UI.
 
 Within each phase, specialized agents run concurrently via BRC (enabled by default for refine, plan, and implement). Here's what a completed pipeline looks like:
diff --git a/docs/development/STRUCTURE.md b/docs/development/STRUCTURE.md
index 9e5f975d20..b04143f3ed 100644
--- a/docs/development/STRUCTURE.md
+++ b/docs/development/STRUCTURE.md
@@ -98,6 +98,8 @@ orchestrator/
 ├── kubernetes_spawner.py   # Agent Job lifecycle (replaces ContainerSpawner)
 ├── kubernetes_monitor.py   # k8s Job state monitoring (replaces ContainerMonitor)
 ├── concurrent_executor.py  # Concurrent phase executor (spawns all agents simultaneously)
+├── slice_scheduler.py      # Wave-based scheduler for the implement-phase slice DAG: computes execution waves, caps concurrency, two-tier max_cycles accounting, failure-cascade detection (#2137)
+├── stacked_pr_reconciler.py # Stacked-PR rebase reconciler: detects child slice PRs whose base branch was deleted after a parent merge and retargets them via gateway rebase_onto (#2137)
 ├── action_guards.py        # Formal BRC state machine action guards (preconditions for propose/ack/nack/confirm/withdraw)
 ├── approval_matrix.py      # Per-reviewer ACK/NACK matrix for BRC consensus
 ├── attestation_schemas.py  # Attestation payload validation for BRC proposals
@@ -324,7 +326,7 @@ shared/
 │   ├── agent_roles.py      # Multi-agent role definitions (all agent and reviewer roles)
 │   ├── orchestrator.py     # Multi-agent orchestration dispatch logic
 │   ├── orchestration.py    # Agent execution state management
-│   ├── dependency_graph.py # Agent dependency resolution for parallel execution
+│   ├── dependency_graph.py # Generic dependency graph (PEP-695 typed): used for agent-role DAGs and for the implement-phase slice DAG (#2137 generification)
 │   ├── plan_parser.py      # Plan document parsing with task extraction and phase dependency normalization
 │   ├── agent_recovery.py   # Failed agent recovery logic
 │   ├── checkpoints.py      # Checkpoint data models
diff --git a/docs/guides/concurrent-execution.md b/docs/guides/concurrent-execution.md
index 26f9fefe83..196ec0ed8d 100644
--- a/docs/guides/concurrent-execution.md
+++ b/docs/guides/concurrent-execution.md
@@ -1,6 +1,8 @@
 # Concurrent Execution Mode
 
-Concurrent execution mode runs all agents for the current pipeline phase simultaneously — all sharing the pipeline branch — rather than sequentially in dependency-ordered waves. Agents communicate via the orchestrator message bus and signal readiness for phase completion via a consensus protocol. BRC consensus is active by default for the **refine**, **plan**, and **implement** phases. Additional phases (such as `review`) can be added via the `concurrent_phases` config.
+Concurrent execution mode runs all agents for the current pipeline phase simultaneously rather than sequentially in dependency-ordered waves. Agents communicate via the orchestrator message bus and signal readiness for phase completion via a consensus protocol. BRC consensus is active by default for the **refine**, **plan**, and **implement** phases. Additional phases (such as `review`) can be added via the `concurrent_phases` config.
+
+**Implement-phase note**: the implement phase no longer runs as a single team on a shared branch. Instead, the plan's tasks are split into a DAG of independent **slices** — each slice runs its own concurrent agent team on its own integration branch. Concurrent execution within each slice follows the BRC protocol described here. See [Slice-DAG Implement Phase](../architecture/slice-dag.md) for the slice-level orchestration model.
 
 This is distinct from the standard wave-based parallel execution (Tier 2), where agents run in dependency order but multiple independent agents execute in parallel within each wave.
 
@@ -44,7 +46,7 @@ When concurrent execution starts, the `ConcurrentPhaseExecutor` (in `orchestrato
 | `plan` | `architect`, `task_planner`, `risk_analyst`, `reviewer_plan` |
 | `implement` | `coder`, `tester`, `documenter`, `reviewer_code`, `reviewer_code_holistic`, `reviewer_contract`, `reviewer_security`, `reviewer_concurrency` |
 
-**Shared branch**: All agents operate on the pipeline's shared branch (e.g., `egg/issue-123`). Agents coordinate commits via the message bus to sequence their work and avoid conflicts.
+**Branch model**: For **refine** and **plan**, all agents operate on the pipeline's shared branch (e.g., `egg/issue-123`) and coordinate commits via the message bus to sequence their work and avoid conflicts. For **implement**, each slice runs on its own integration branch (`egg/issue-N/slice-M`); the shared-branch coordination described below applies *within* a slice's agent team — see [Slice-DAG Implement Phase](../architecture/slice-dag.md).
 
 **Environment injection**: Each concurrent agent receives:
 
@@ -857,12 +859,12 @@ Each concurrent agent runs in its own isolated git worktree. This prevents agent
 
 **Architecture:**
 - Each agent pod receives a unique worktree created by the gateway, keyed by Job name (not pipeline ID)
-- All agents push to the same shared pipeline branch (e.g., `egg/issue-{N}`)
+- For **refine** and **plan**, all agents push to the same shared pipeline branch (e.g., `egg/issue-{N}`); for **implement**, all agents within a slice push to that slice's integration branch (`egg/issue-{N}/slice-{M}`) — see [Slice-DAG Implement Phase](../architecture/slice-dag.md)
 - Git worktrees share the object store — only working tree files are duplicated, so disk overhead is marginal
 
 **Push coordination (pull-before-push):**
 1. Agent finishes work, commits in its own worktree
-2. Agent pushes to the shared branch via the gateway
+2. Agent pushes to the team's branch (pipeline branch for refine/plan, slice integration branch for implement) via the gateway
 3. If push is rejected (another agent pushed first) → `git pull --rebase` → retry push
 4. Rebase **cannot conflict** because agents have mutually exclusive file write permissions (see [Agent Roles Reference](../reference/agent-roles.md))
 
@@ -872,7 +874,7 @@ This works because role restrictions guarantee non-overlapping file sets (coder
 
 ### Reviewer Worktree Sync
 
-Per-agent worktrees are created at phase start from the pipeline branch. When a producer pushes commits and proposes, the reviewer's worktree does not automatically have those commits. To address this, the BRC preamble instructs reviewers to sync their worktree before reviewing:
+Per-agent worktrees are created at phase start from the team's branch — the pipeline branch for refine/plan, the slice integration branch for each implement slice. When a producer pushes commits and proposes, the reviewer's worktree does not automatically have those commits. To address this, the BRC preamble instructs reviewers to sync their worktree before reviewing:
 
 ```bash
 git fetch origin && git merge origin/{branch} --no-edit
diff --git a/docs/guides/sdlc-pipeline.md b/docs/guides/sdlc-pipeline.md
index ea2c405500..f4e1f052c6 100644
--- a/docs/guides/sdlc-pipeline.md
+++ b/docs/guides/sdlc-pipeline.md
@@ -294,7 +294,9 @@ The contract tracks per-reviewer verdicts for debugging:
 
 ### Multi-Agent Orchestration
 
-The implement phase uses concurrent BRC execution, where specialized agents run simultaneously and coordinate via the message bus.
+The implement phase runs as a **DAG of independent slices** (#2137). Each slice has its own integration branch (`egg/issue-N/slice-M`), agent team, BRC consensus, and stacked PR targeting the parent slice's branch (or the pipeline branch for root slices). The `SliceScheduler` computes execution waves — slices whose dependencies are satisfied run concurrently (capped at `EGG_ORCH_MAX_PARALLEL_SLICES`, default 5); dependent slices wait in subsequent waves. See [Slice-DAG Implement Phase](../architecture/slice-dag.md) for the full model including forest validation, two-tier `max_cycles` accounting, failure cascade, and the stacked-PR reconciler.
+
+Within each slice, concurrent BRC execution runs: specialized agents run simultaneously and coordinate via the message bus.
 
 **Agent Roles:**
 
@@ -1357,14 +1359,18 @@ all changes.
 **Reviewer (code/contract)**: Reviews committed code or contract artifacts. Polls for
 `PROGRESS` from coder. Signals `READY` after review is complete.
 
-### Shared Pipeline Branch
+### Branch Model
+
+For the **refine** and **plan** phases, all concurrent agents operate on the pipeline's
+shared branch (e.g., `egg/issue-999`) — they commit directly to a single shared history
+and coordinate via the message bus to sequence commits and avoid conflicts (for example,
+the coder signals `HANDOFF` when its changes are committed so downstream agents know it
+is safe to pull and build on top).
 
-All concurrent agents operate on the pipeline's shared branch (e.g., `egg/issue-999`).
-Rather than each agent having an isolated worktree branch, all agents commit directly
-to a single shared history. Agents coordinate via the message bus to sequence commits
-and avoid conflicts — for example, the coder signals `HANDOFF` when its changes are
-committed so downstream agents (tester, documenter) know it is safe to pull and build
-on top.
+For the **implement** phase, the pipeline branch is no longer shared across the whole
+team. Tasks are split into a DAG of slices, and each slice runs on its own integration
+branch (`egg/issue-999/slice-M`); the shared-history coordination above applies *within*
+a slice's agent team. See [Slice-DAG Implement Phase](../architecture/slice-dag.md).
 
 ### Failure Handling
 
@@ -1436,11 +1442,11 @@ identify blocked or stuck agents.
 **Message bus empty**: Verify the pipeline has `concurrent_execution: true` in its
 config. The message bus is only active for concurrent pipelines.
 
-**Commit conflicts**: Since all concurrent agents share a single branch, agents
-coordinate commits via the message bus to avoid conflicts. If an agent encounters a
-conflict when pushing, it should pull, rebase, and retry. If conflicts persist, the
-agent signals `BLOCKED` and a HITL decision is created. Consider adding role-based
-file restrictions to minimize overlap.
+**Commit conflicts**: Within a single team's branch (the pipeline branch for refine/plan,
+or a slice's integration branch for implement), concurrent agents coordinate commits via
+the message bus to avoid conflicts. If an agent encounters a conflict when pushing, it
+should pull, rebase, and retry. If conflicts persist, the agent signals `BLOCKED` and a
+HITL decision is created. Consider adding role-based file restrictions to minimize overlap.
 
 ## Agent MCP tools (`EGG_MCP_TOOLS` flag)
 
diff --git a/docs/reference/orchestrator-cli.md b/docs/reference/orchestrator-cli.md
index a0d0205ef1..c76f54e0b1 100644
--- a/docs/reference/orchestrator-cli.md
+++ b/docs/reference/orchestrator-cli.md
@@ -79,6 +79,11 @@ Agent role can be omitted when `EGG_AGENT_ROLE` is set.
 | `EGG_ORCH_STATE_STORE_PROBE_INTERVAL` | Cadence (seconds) of the background state-store self-heal probe. Default `15`. Lowering tightens wedge-detection at the cost of more frequent `git` calls; raising it does the inverse. The staleness watchdog flips `/api/v1/ready` to 503 when cache age exceeds `interval × 2`, so this setting also controls the readiness-flap window. Values above ~30s can exceed the readinessProbe's boot tolerance (`initialDelaySeconds + periodSeconds × failureThreshold = 35s`). |
 | `EGG_ORCH_WAITRESS_THREADS` | Waitress WSGI thread pool size. Default `16`, minimum `4`. Values `< 4` cause the orchestrator to `sys.exit(78)` (EX_CONFIG) at boot with an ERROR log. Each blocking long-poll occupies one thread; size the pool above the concurrent-agent count plus short-request headroom. The `egg_inflight_long_polls` Prometheus gauge exposes saturation. See [Agent Wait Patterns §7](agent-wait-patterns.md#7-egg_orch_waitress_threads--thread-pool--long-poll-coupling). |
 | `EGG_HEARTBEAT_RATE_LIMIT` | Per-`(pipeline_id, agent_role)` `HEARTBEAT` rate cap (messages per minute). Default `20`. Exceeding returns HTTP 429 with a `Retry-After` header; the CLI surfaces 429 as exit 3 (permanent). See [Agent Wait Patterns §5](agent-wait-patterns.md#5-egg_heartbeat_rate_limit--per-role-heartbeat-cap). |
+| `EGG_ORCH_MAX_PARALLEL_SLICES` | Maximum number of implement-phase slices that may run concurrently within a single pipeline wave. Default `5`. Backed by `SliceScheduler.max_parallel_slices`; reduce when container or gateway resources are constrained. |
+| `EGG_ORCH_SLICE_LOCAL_MAX_CYCLES` | Per-slice BRC re-proposal ceiling before HITL escalation. Default `3`. Part of the two-tier cycle cap model (#2137 decision-9). *API live, not yet wired in the run loop — see [Slice-DAG Implement Phase](../architecture/slice-dag.md); #2199.* |
+| `EGG_ORCH_SLICE_GLOBAL_MAX_CYCLES` | Pipeline-wide cap on the summed total of slice re-proposal cycles. Default `10`. Either the local or global cap tripping escalates to HITL. *API live, not yet wired in the run loop — see [Slice-DAG Implement Phase](../architecture/slice-dag.md); #2199.* |
+| `EGG_ORCH_SLICE_FAILURE_GRACE_SECONDS` | Grace window (seconds) between a slice failure and the orchestrator marking the downstream subtree `BLOCKED_ON_FAILED_DEPENDENCY`. Default `60`. Allows HITL resolution before the cascade fires. |
+| `EGG_ORCH_STACKED_PR_RECONCILER_INTERVAL_SECONDS` | Polling cadence (seconds) of the stacked-PR reconciler that detects child slice PRs whose base branch was deleted after a parent merge. Default `30`. |
 | `AGENT_ANCHOR_ID` | Agent anchor ID (`{role}-{short_container_id}`), auto-set by container spawner |
 | `EGG_LIFECYCLE_SECRET` | Bearer token required for lifecycle-control endpoints (HITL resolve/cancel, pipeline CRUD, phase overrides, container spawn/stop). Stored at `~/.config/egg/lifecycle-secret`. Must be exported in the human's shell to run `egg-orch decision resolve`, `egg-orch pipeline delete`, etc. Agent pods never receive it (see #1769). |