## Problem / Motivation Replay/debug token data uses two complementary deduplication markers today: - `@prev` (`ProcessDebugger::TOKEN_DATA_PREV`) collapses a whole step when its entire token stack is identical to the previous step. - `@ref` (`ProcessDebugger::TOKEN_DATA_REF`) collapses, **within a single step**, a content entity that appears under more than one token name, keyed on `entityType:UUID` (see #3590332). This asserts identity within one synchronous snapshot. Neither catches a very common pattern: the **same entity carried unchanged across several steps** (but where other tokens differ, so `@prev` does not fire), and **nested referenced entities** that repeat the same sub-tree many times within and across steps. The original 738 MB sample (#3590324) was dominated by entity-reference chains (`campaign_id -> created_id -> employer_id -> ...`) and `owner -> user_picture -> owner` repetition re-serializing identical sub-trees at every level and every step. The depth cap + cycle guard (#3590324) bounds the recursion, but identical sub-trees are still serialized in full wherever they legitimately appear. We cannot assume an entity is unchanged across steps from its UUID alone — a step may mutate a field, and the debugger must show the new value. The only safe signal is **equality of the fully-normalized sub-tree**, which we can only know after normalizing it. ## Proposed resolution Introduce a third, content-equality marker (working name `@same`, `ProcessDebugger::TOKEN_DATA_SAME`) that deduplicates **fully-normalized sub-trees** by content hash, across steps and at any nesting level: - During normalization, compute a hash of each normalized sub-tree **bottom-up** (a Merkle-style rolling hash: a node's hash folds in its children's hashes), so the whole-tree traversal already performed for normalization yields all sub-tree hashes at essentially no extra cost. - Maintain a cross-step index `normalizedHash -> firstOccurrence`, where `firstOccurrence` locates the first emission unambiguously by **(stepIndex, path)** (richer than `@ref`, which points at a sibling token key in the same step). - When a later sub-tree (top-level token or nested referenced entity) hashes identically to a recorded one, emit `{ label, token, '@same': { step, path } }` instead of repeating the sub-tree. - **Robustness:** to eliminate hash-collision risk, keep the first full sub-tree available and verify structural equality on a hash match before collapsing (the dedup added in #3585592 taught us that a dedup which silently fails or mis-fires is worse than none). The marker is owned by ECA (the model owner); `modeler_api` already passes replay data through verbatim (#3588498); the Workflow Modeler must learn to resolve `@same` at display time (companion modeler issue, cross-linked below), alongside the existing `@ref`/`@prev` lazy expansion (#3589096). ## Relationship to existing markers | Marker | Scope | Asserts | Key | |--------|-------|---------|-----| | `@prev` | whole step vs previous step | entire token stack unchanged | step-level equality | | `@ref` | within one step | identity (same object now) | `entityType:UUID` | | `@same` (new) | sub-tree, across steps + nested | content equality (proven by hash) | normalized-content hash | ## Remaining tasks - [ ] Compute bottom-up (Merkle-style) hashes of normalized sub-trees during normalization in `Drupal\eca\Token\Browser`. - [ ] Add `ProcessDebugger::TOKEN_DATA_SAME` and a cross-step first-occurrence index keyed by content hash, referencing (step, path). - [ ] Verify structural equality on hash match before collapsing (collision-safe). - [ ] Apply to nested referenced entities, not just top-level tokens. - [ ] Keep `expandHistory()`/`expandRefs()` semantics intact; `@same` expansion is frontend-only (compact markers stay on the wire and in exports). - [ ] Tests (unit + kernel): unchanged entity across steps collapses; a mutated entity does NOT collapse; nested identical referenced entity collapses; collision verification path. - [ ] Coordinate the marker-contract/version bump with the modeler companion issue. ## Related - Parent: project/eca#3590324 - Builds on: #3590332 (defer expansion + UUID-keyed per-step dedup), #3585592 (introduced @ref/@prev) - Companion (frontend resolver for `@same`): modeler issue cross-linked below.