diff --git a/docs/specification.md b/docs/specification.md
index dbe7bd381..9a7036f41 100644
--- a/docs/specification.md
+++ b/docs/specification.md
@@ -45561,6 +45561,87 @@ When advanced features are unavailable, the system gracefully degrades. The pipe
 3. Try `semantic-embedding` (requires vector) -> if unavailable:
 4. Fall back to `simple-keyword` (requires only text search / ripgrep)
 
+#### Context Tier Hydration
+
+Before context assembly can occur, the `ContextTierService` must be populated with file fragments from the plan's linked project resources. This is the responsibility of the **context tier hydrator** — a module that bridges the Resource Registry (files on disk) and the ACMS context tier (in-memory fragments).
+
+##### Module: `context_tier_hydrator`
+
+**Location**: `src/cleveragents/application/services/context_tier_hydrator.py`
+
+The hydrator exposes two public functions:
+
+```python
+def hydrate_tiers_for_plan(
+    tier_service: ContextTierService,
+    project_names: list[str],
+    project_repository: ProjectRepository,
+    resource_registry: ResourceRegistry,
+) -> int:
+    """Hydrate all projects linked to a plan into the tier service.
+
+    Returns the total number of fragments stored across all projects.
+    """
+
+def hydrate_tiers_from_project(
+    tier_service: ContextTierService,
+    project_name: str,
+    resource_id: str,
+    resource_location: str,
+    resource_type: str,
+) -> int:
+    """Hydrate a single project resource into the tier service.
+
+    Returns the number of fragments stored for this resource.
+    """
+```
+
+##### File Listing Strategy
+
+The hydrator uses a resource-type-aware file listing strategy:
+
+| Resource Type | Strategy | Notes |
+|---|---|---|
+| `git-checkout` | `git ls-files` | Lists only tracked files; respects `.gitignore` automatically |
+| All others | `os.walk` | Recursive filesystem traversal |
+
+##### Size and Budget Limits
+
+The hydrator enforces per-resource budget limits to prevent unbounded memory consumption:
+
+| Limit | Value | Scope |
+|---|---|---|
+| Maximum file size | 256 KB (262,144 bytes) | Per file — files exceeding this limit are skipped |
+| Maximum total size | 10 MB (10,485,760 bytes) | Per project resource — hydration stops when this is reached |
+
+Files in common non-source directories are automatically skipped: `.git/`, `node_modules/`, `__pycache__/`, `.tox/`, `.venv/`, `dist/`, `build/`, `.mypy_cache/`, `.pytest_cache/`. Binary files (detected by null-byte presence in the first 8 KB) are also skipped.
+
+##### Fragment Structure
+
+Each file produces one `TieredFragment` stored in `ContextTierService` with:
+
+| Field | Value | Notes |
+|---|---|---|
+| `tier` | `ContextTier.HOT` | All hydrated fragments start in the hot tier |
+| `content` | File text content | UTF-8 decoded, errors replaced |
+| `metadata["path"]` | Relative file path | Relative to the resource root |
+| `metadata["detail_depth"]` | `"10"` | Stored as a **string** (not int) |
+| `metadata["relevance_score"]` | `"1.0"` | Stored as a **string** (not float) |
+
+!!! warning "String Metadata Values"
+    `detail_depth` and `relevance_score` are stored as strings, not numeric types. This is intentional — the metadata dict is typed as `dict[str, str]` in `TieredFragment`. Consumers that need numeric values must parse them explicitly.
+
+##### Integration Point
+
+Hydration runs **before context assembly** in `LLMExecuteActor.execute()`. The call sequence is:
+
+1. `LLMExecuteActor.execute()` is invoked with the current plan and project list.
+2. `hydrate_tiers_for_plan(tier_service, project_names, ...)` is called to populate `ContextTierService`.
+3. The ACMS Context Assembly Pipeline runs, reading from the now-populated `ContextTierService`.
+4. The assembled context is injected into the LLM prompt.
+
+Without this hydration step, `ContextTierService` starts empty on every CLI invocation, leaving the LLM with zero file context during plan execution. This was the root cause of bug #1028.
+
 #### ACMS Performance Characteristics
 
 ##### Assembly Latency