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+# Resizable Model Activity Timeline and Dense CTE Plan Design
+
+**Date:** 2026-07-15
+
+## Goal
+
+Restore the left **Model activity** panel as a readable chronological view of the original
+question, model reasoning, and model response; make the panel width adjustable with the mouse;
+and substantially reduce the perceived vertical padding of F6 CTE cards while retaining useful
+horizontal breathing room.
+
+This design supersedes the left-panel visibility and CTE-density sections of
+`2026-07-15-central-live-log-cte-density-design.md`. The compact central live log remains in
+place. Backend, SSE, workflow, persistence, and model-provider contracts do not change.
+
+## Root causes
+
+The session store and stream already retain all three events required by the panel:
+
+- the submitted question is appended to `activityLog` as `prompt`;
+- chain-of-thought/model reasoning arrives through `activity_delta` as `thinking`;
+- the streamed model response arrives through `text_delta` as `assistant`.
+
+The regression is at the rendering boundary. `ModelActivityPanel` currently allows only
+`thinking` and `status`, so it explicitly hides the question and model response while admitting
+the `F1 STATUS INFO` rows the user does not want.
+
+The panel/conversation split is also fixed in two separate components: the panel uses `w-2/5` and
+the conversation uses `w-3/5`. There is no separator, resize state, pointer handling, keyboard
+interaction, clamping, responsive fallback, or persistence.
+
+The shared `Card` primitive is not secretly adding height to F6: `CtePlanViewer` already overrides
+its root padding and gaps. The remaining perceived vertical excess is mainly caused by a 20 px
+content gap, repeated 8 px heading margins, relaxed line heights, and table/filter rows with 8 px
+padding on both vertical edges.
+
+## Model activity projection
+
+The left panel uses an explicit, default-deny allowlist:
+
+| Activity kind | Visible | Presentation |
+| --- | --- | --- |
+| `prompt` | Yes | **Question** label and readable body. |
+| `thinking` | Yes | **Reasoning** label and Markdown body in a quieter tone. |
+| `assistant` | Yes | **Response** label and Markdown body. |
+| `status` | No | Excluded, including neutral, warning, and error entries. |
+| `tool` | No | Low-level implementation detail. |
+| `gate` | No | The corresponding form or artifact remains central. |
+| `lifecycle` | No | Process/turn implementation detail. |
+| unknown future kinds | No | Default-deny prevents accidental exposure. |
+
+Visible entries keep their existing chronological order. The panel does not reconstruct or merge
+separate data sources: it filters the authoritative in-memory `activityLog`. This preserves the
+actual interleaving of question, reasoning, and response.
+
+Each visible entry is rendered as a compact semantic row with a human-facing label instead of raw
+kind/status/level metadata. Phase is shown only when present and visually subordinate to the
+label. `prompt`, `thinking`, and `assistant` bodies support Markdown and long-value wrapping.
+Rows use an 8 px vertical rhythm rather than the current 12 px. The panel follows appended visible
+content only while the reader is already near the bottom; manual upward scrolling remains stable.
+
+The central live log continues to show the assistant transcript while the model is working. Its
+small bounded scrolling box is intentionally retained, even though assistant output is also
+available in the full left timeline: the two surfaces serve different purposes, glanceable current
+progress centrally and complete readable activity history on demand.
+
+## Resizable split
+
+On desktop, the fixed percentage widths are replaced by one width owned by `AppShell` and applied
+to the left panel. The conversation column consumes the remaining space with `flex-1 min-w-0`.
+
+The split contract is:
+
+- default panel width: 384 px;
+- minimum panel width: 288 px;
+- maximum panel width: the smaller of 576 px and `containerWidth - 512 px`;
+- minimum central width: 512 px whenever the container is wide enough to satisfy both minima;
+- stored width is clamped again whenever container geometry changes.
+
+A full-height vertical separator sits between the panel and central column. Its visible line stays
+subtle, while a 12–16 px transparent hit area makes it easy to acquire. Hover, focus, and active
+drag strengthen the divider. The cursor is `col-resize`, text selection is suppressed during a
+drag, and pointer capture keeps the interaction stable when the pointer leaves the hit area.
+
+The separator is keyboard operable and exposes `role="separator"`, vertical orientation, current
+value, and min/max values:
+
+- Left/Right changes width by 16 px;
+- Shift+Left/Right changes width by 48 px;
+- Home moves to the minimum;
+- End moves to the maximum.
+
+The last committed width is persisted globally in browser `localStorage` after pointer release or
+keyboard interaction. It is not stored per session and never reaches the backend. Closing the
+panel remains ephemeral; reopening it in the same or a later browser session restores the clamped
+saved width.
+
+Below the desktop breakpoint, resizing is disabled and the activity panel becomes a bounded
+overlay drawer, up to 90 viewport percent and 384 px wide. The central area remains full width,
+preventing the two minimum widths from creating overflow on narrow screens.
+
+## Compact CTE plan
+
+The change remains local to `CtePlanViewer`; the shared `Card` component, content schema, and grid
+topology do not change. Horizontal padding stays at 12 px below `sm` and 16 px from `sm` upward.
+
+Vertical density changes target the actual sources of height:
+
+- header title/purpose gap: 12 px to 8 px;
+- body section gap: 20 px to 12 px;
+- dependency/key grid gap: 16 px to 12 px;
+- repeated section heading margin: 8 px to 4 px;
+- table and filter row padding: 8 px to 4 px per vertical edge;
+- filter internal spacing: 12 px to 8 px;
+- filter grid gap: 12 px to 8 px;
+- filter detail gap and divider padding: reduced to 4 px;
+- rationale divider padding and heading margin: reduced to 4 px;
+- relaxed line heights inside dense rows: replaced by compact fixed line heights.
+
+Header and main content outer padding remain 8 px per vertical edge so the card border does not
+feel cramped. Chips, badges, borders, long-identifier wrapping, semantic sections, and the 12 px
+gap between distinct CTE cards stay unchanged.
+
+## Error and edge-case behavior
+
+- If a provider emits no `thinking`, the question and response still render in the panel.
+- If assistant text has not arrived yet, the question and available reasoning still render.
+- Hidden status/tool/gate/lifecycle events do not affect the panel empty state or scroll-follow.
+- Unknown activity kinds remain hidden.
+- A corrupt or unavailable stored width falls back to 384 px.
+- A formerly valid stored width is clamped after viewport or container resizing.
+- When the container cannot satisfy both desktop minima, the responsive overlay behavior prevents
+  horizontal overflow.
+- Long Markdown, SQL identifiers, table names, filters, and rationales wrap without horizontal
+  scrolling.
+
+## Testing and verification
+
+Frontend RED/GREEN tests must prove:
+
+1. A mixed activity sequence renders only `prompt`, `thinking`, and `assistant`, in chronological
+   order, with human-facing labels; status, tool, gate, lifecycle, and unknown kinds remain hidden.
+2. Prompt and assistant bodies use the readable Markdown path, thinking keeps its quieter tone,
+   and hidden updates cannot trigger bottom-follow.
+3. The panel's empty state and existing near-bottom follow behavior are based only on visible
+   entries.
+4. The desktop split starts at 384 px, clamps to its computed min/max, updates through pointer
+   capture, and gives the central column the remaining width.
+5. The separator exposes the required ARIA values and supports arrows, Shift+arrows, Home, and End.
+6. Valid saved widths are restored; corrupt or out-of-range values fall back or clamp safely.
+7. The narrow-screen layout uses an overlay drawer and does not compress the central column.
+8. CTE cards retain their semantic structure and horizontal padding while exact vertical gaps,
+   row padding, margins, and line heights match the compact contract.
+
+Verification runs the focused activity-panel, AppShell/split, and CTE viewer tests first, followed
+by the complete frontend Vitest suite, `npx tsc -b`, `npm run build`, the Impeccable layout detector,
+and `git diff --check`.
+
+## Deployment
+
+Only the frontend is affected. Rebuild and force-recreate only the frontend Compose service. If
+and only if the Vite entry hash changes, restart the portal web container to invalidate its cached
+manifest. Do not restart the core/backend or terminate an unrelated active Pi session. Verify the
+running frontend image and entry hash, container health, and that the core start timestamp is
+unchanged.
+
+## Out of scope
+
+- Removing any event kind from `activityLog` or changing the session store fold.
+- Backend, SSE, replay, persistence, workflow, or model-provider changes.
+- Showing status, tool, gate, lifecycle, or unknown events in the left panel.
+- Removing or expanding the compact central live log.
+- Per-session or backend persistence of panel width.
+- Changing CTE content, ordering, colors, schema, or the shared card design system.