can1357
2e45297c43
- Moved documentation files from packages/coding-agent/docs/ to root docs/ directory to flatten the documentation structure. - Updated all internal documentation links to account for the new file locations, adjusting relative paths to maintain correct references across the monorepo. - Updated README.md and issue template configuration to reference documentation at the new root docs/ location instead of packages/coding-agent/docs/.
191 lines
8.0 KiB
Markdown
191 lines
8.0 KiB
Markdown
# Session tree architecture (current)
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Reference: [session.md](../docs/session.md)
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This document describes how session tree navigation works today: in-memory tree model, leaf movement rules, branching behavior, and extension/event integration.
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## What this subsystem is
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The session is stored as an append-only entry log, but runtime behavior is tree-based:
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- Every non-header entry has `id` and `parentId`.
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- The active position is `leafId` in `SessionManager`.
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- Appending an entry always creates a child of the current leaf.
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- Branching does **not** rewrite history; it only changes where the leaf points before the next append.
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Key files:
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- `src/session/session-manager.ts` — tree data model, traversal, leaf movement, branch/session extraction
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- `src/session/agent-session.ts` — `/tree` navigation flow, summarization, hook/event emission
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- `src/modes/components/tree-selector.ts` — interactive tree UI behavior and filtering
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- `src/modes/controllers/selector-controller.ts` — selector orchestration for `/tree` and `/branch`
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- `src/modes/controllers/input-controller.ts` — command routing (`/tree`, `/branch`, double-escape behavior)
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- `src/session/messages.ts` — conversion of `branch_summary`, `compaction`, and `custom_message` entries into LLM context messages
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## Tree data model in `SessionManager`
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Runtime indices:
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- `#byId: Map<string, SessionEntry>` — fast lookup for any entry
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- `#leafId: string | null` — current position in the tree
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- `#labelsById: Map<string, string>` — resolved labels by target entry id
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Tree APIs:
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- `getBranch(fromId?)` walks parent links to root and returns root→node path
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- `getTree()` returns `SessionTreeNode[]` (`entry`, `children`, `label`)
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- parent links become children arrays
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- entries with missing parents are treated as roots
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- children are sorted oldest→newest by timestamp
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- `getChildren(parentId)` returns direct children
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- `getLabel(id)` resolves current label from `labelsById`
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`getTree()` is a runtime projection; persistence remains append-only JSONL entries.
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## Leaf movement semantics
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There are three leaf movement primitives:
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1. `branch(entryId)`
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- Validates entry exists
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- Sets `leafId = entryId`
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- No new entry is written
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2. `resetLeaf()`
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- Sets `leafId = null`
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- Next append creates a new root entry (`parentId = null`)
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3. `branchWithSummary(branchFromId, summary, details?, fromExtension?)`
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- Accepts `branchFromId: string | null`
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- Sets `leafId = branchFromId`
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- Appends a `branch_summary` entry as child of that leaf
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- When `branchFromId` is `null`, `fromId` is persisted as `"root"`
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## `/tree` navigation behavior (same session file)
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`AgentSession.navigateTree()` is navigation, not file forking.
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Flow:
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1. Validate target and compute abandoned path (`collectEntriesForBranchSummary`)
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2. Emit `session_before_tree` with `TreePreparation`
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3. Optionally summarize abandoned entries (hook-provided summary or built-in summarizer)
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4. Compute new leaf target:
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- selecting a **user** message: leaf moves to its parent, and message text is returned for editor prefill
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- selecting a **custom_message**: same rule as user message (leaf = parent, text prefills editor)
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- selecting any other entry: leaf = selected entry id
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5. Apply leaf move:
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- with summary: `branchWithSummary(newLeafId, ...)`
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- without summary and `newLeafId === null`: `resetLeaf()`
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- otherwise: `branch(newLeafId)`
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6. Rebuild agent context from new leaf and emit `session_tree`
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Important: summary entries are attached at the **new navigation position**, not on the abandoned branch tail.
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## `/branch` behavior (new session file)
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`/branch` and `/tree` are intentionally different:
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- `/tree` navigates within the current session file.
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- `/branch` creates a new session branch file (or in-memory replacement for non-persistent mode).
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User-facing `/branch` flow (`SelectorController.showUserMessageSelector` → `AgentSession.branch`):
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- Branch source must be a **user message**.
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- Selected user text is extracted for editor prefill.
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- If selected user message is root (`parentId === null`): start a new session via `newSession({ parentSession: previousSessionFile })`.
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- Otherwise: `createBranchedSession(selectedEntry.parentId)` to fork history up to the selected prompt boundary.
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`SessionManager.createBranchedSession(leafId)` specifics:
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- Builds root→leaf path via `getBranch(leafId)`; throws if missing.
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- Excludes existing `label` entries from copied path.
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- Rebuilds fresh label entries from resolved `labelsById` for entries that remain in path.
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- Persistent mode: writes new JSONL file and switches manager to it; returns new file path.
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- In-memory mode: replaces in-memory entries; returns `undefined`.
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## Context reconstruction and summary/custom integration
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`buildSessionContext()` (in `session-manager.ts`) resolves the active root→leaf path and builds effective LLM context state:
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- Tracks latest thinking/model/mode/ttsr state on path.
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- Handles latest compaction on path:
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- emits compaction summary first
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- replays kept messages from `firstKeptEntryId` to compaction point
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- then replays post-compaction messages
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- Includes `branch_summary` and `custom_message` entries as `AgentMessage` objects.
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`session/messages.ts` then maps these message types for model input:
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- `branchSummary` and `compactionSummary` become user-role templated context messages
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- `custom`/`hookMessage` become user-role content messages
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So tree movement changes context by changing the active leaf path, not by mutating old entries.
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## Labels and tree UI behavior
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Label persistence:
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- `appendLabelChange(targetId, label?)` writes `label` entries on the current leaf chain.
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- `labelsById` is updated immediately (set or delete).
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- `getTree()` resolves current label onto each returned node.
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Tree selector behavior (`tree-selector.ts`):
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- Flattens tree for navigation, keeps active-path highlighting, and prioritizes displaying the active branch first.
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- Supports filter modes: `default`, `no-tools`, `user-only`, `labeled-only`, `all`.
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- Supports free-text search over rendered semantic content.
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- `Shift+L` opens inline label editing and writes via `appendLabelChange`.
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Command routing:
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- `/tree` always opens tree selector.
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- `/branch` opens user-message selector unless `doubleEscapeAction=tree`, in which case it also uses tree selector UX.
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## Extension and hook touchpoints for tree operations
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Command-time extension API (`ExtensionCommandContext`):
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- `branch(entryId)` — create branched session file
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- `navigateTree(targetId, { summarize? })` — move within current tree/file
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Events around tree navigation:
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- `session_before_tree`
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- receives `TreePreparation`:
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- `targetId`
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- `oldLeafId`
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- `commonAncestorId`
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- `entriesToSummarize`
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- `userWantsSummary`
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- may cancel navigation
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- may provide summary payload used instead of built-in summarizer
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- receives abort `signal` (Escape cancellation path)
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- `session_tree`
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- emits `newLeafId`, `oldLeafId`
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- includes `summaryEntry` when a summary was created
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- `fromExtension` indicates summary origin
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Adjacent but related lifecycle hooks:
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- `session_before_branch` / `session_branch` for `/branch` flow
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- `session_before_compact`, `session.compacting`, `session_compact` for compaction entries that later affect tree-context reconstruction
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## Real constraints and edge conditions
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- `branch()` cannot target `null`; use `resetLeaf()` for root-before-first-entry state.
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- `branchWithSummary()` supports `null` target and records `fromId: "root"`.
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- Selecting current leaf in tree selector is a no-op.
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- Summarization requires an active model; if absent, summarize navigation fails fast.
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- If summarization is aborted, navigation is cancelled and leaf is unchanged.
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- In-memory sessions never return a branch file path from `createBranchedSession`.
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## Legacy compatibility still present
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Session migrations still run on load:
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- v1→v2 adds `id`/`parentId` and converts compaction index anchor to id anchor
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- v2→v3 migrates legacy `hookMessage` role to `custom`
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Current runtime behavior is version-3 tree semantics after migration.
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