feat(ui): documents open in an almost-fullscreen modal instead of a new page — same-page overlay on chat + Sources, /document.html kept as the no-JS/direct-link fallback

tests/e2e/test_document_back_navigation.py

@@ -6,21 +6,26 @@ Run in isolation (DB must be up: ``podman compose up -d db``):
 
     uv run pytest tests/e2e/test_document_back_navigation.py -v --no-cov
 
-Both entry points (chat source chips, Sources table links) open the viewer
-in a NEW tab, where there is no browser history — so the return target is
-carried in the viewer URL: chat chips append ``&back=%2F`` (resolves to
-"Chat"), Sources links omit the param (the viewer's default
-``/sources.html`` applies → "Sources"). The viewer only honors
-same-origin relative ``back`` values; everything else falls back to
-``/sources.html``.
+The viewer can be reached directly (no browser history to go back to),
+so the return target is carried in the viewer URL: chat chips append
+``&back=%2F`` (resolves to "Chat"), Sources links omit the param (the
+viewer's default ``/sources.html`` applies → "Sources"). The viewer only
+honors same-origin relative ``back`` values; everything else falls back
+to ``/sources.html``.
+
+Phase 26 adaptation: the chip/row-link LEFT click now opens the
+document in the same-page modal — no new tab is spawned. The encoded
+viewer URL survives as each link's ``href`` (the no-JS / context-menu
+"open in new tab" escape hatch), so the back contract is asserted on
+that exact href and verified by navigating to it directly.
 
 Test → story mapping (Playwright Mapping Rule):
-1. ``test_back_from_chat_returns_to_chat`` — question → source chip →
-   new tab with ``&back=%2F`` → back link href ``/`` labeled "Chat" →
-   click → the chat page.
-2. ``test_back_from_sources_returns_to_sources`` — Sources table link →
-   new tab without a ``back`` param → back link href ``/sources.html``
-   labeled "Sources" → click → the Sources page.
+1. ``test_back_from_chat_returns_to_chat`` — question → source chip href
+   (carries ``&back=%2F``) → viewer back link href ``/`` labeled "Chat"
+   → click → the chat page.
+2. ``test_back_from_sources_returns_to_sources`` — Sources table link
+   href (no ``back`` param) → back link href ``/sources.html`` labeled
+   "Sources" → click → the Sources page.
 3. ``test_malicious_back_param_is_rejected`` — absolute,
    protocol-relative, and ``javascript:`` ``back`` values all fall back
    to ``/sources.html`` (labeled "Sources", navigable).
@@ -106,30 +111,33 @@ def test_back_from_chat_returns_to_chat(
 
     chip = page.locator(".msg.brain .source-chip", has_text="kubernetes.md")
     expect(chip).to_have_count(1, timeout=30_000)
-    # Chat chips carry back=/ (encoded %2F) so the viewer knows where home is.
+    # Chat chips carry back=/ (encoded %2F) so the viewer knows where
+    # home is. Phase 26: the left click opens the same-page modal (no
+    # target=_blank); this href is what the no-JS / context-menu "open
+    # in a new tab" path reaches, so the back contract rides on it.
     expect(chip.first).to_have_attribute(
         "href", f"/document.html?source={DOC_SOURCE}&path={DOC_PATH}&back=%2F"
     )
+    expect(chip.first).not_to_have_attribute("target")  # phase 26: modal, not a new tab
 
-    with page.expect_popup() as popup_info:
-        chip.first.click()
-    viewer = popup_info.value
-    expect(viewer).to_have_url(
+    # The exact href asserted above (the no-JS / new-tab escape hatch).
+    page.goto(f"{app_url}/document.html?source={DOC_SOURCE}&path={DOC_PATH}&back=%2F")
+    expect(page).to_have_url(
         re.compile(
             re.escape(f"{app_url}/document.html?source={DOC_SOURCE}&path={DOC_PATH}&back=%2F")
         )
     )
     # The cited document actually rendered (this is the viewer, not an error).
-    expect(viewer.locator("#doc-title")).to_have_text(DOC_TITLE)
+    expect(page.locator("#doc-title")).to_have_text(DOC_TITLE)
     # Back link resolved to the chat page, labeled "Chat".
-    back = viewer.locator("#doc-back")
+    back = page.locator("#doc-back")
     expect(back).to_have_attribute("href", "/")
     expect(back).to_have_text("Chat")
 
     # Click: deterministic anchor navigation back to the chat page.
     back.click()
-    expect(viewer).to_have_url(f"{app_url}/")
-    expect(viewer.locator("#composer")).to_be_visible()
+    expect(page).to_have_url(f"{app_url}/")
+    expect(page.locator("#composer")).to_be_visible()
 
 
 # ---------------------------------------------------------------------------
@@ -148,24 +156,25 @@ def test_back_from_sources_returns_to_sources(
     link = row.locator("td:nth-child(2) a.doc-link")
     expect(link).to_have_count(1)
     # Sources links carry NO back param — the viewer's default target
-    # (/sources.html) applies.
+    # (/sources.html) applies. Phase 26: left click opens the modal;
+    # the href (no back param) is the no-JS / new-tab escape hatch.
     expect(link).to_have_attribute(
         "href", f"/document.html?source={DOC_SOURCE}&path={DOC_PATH}"
     )
+    expect(link).not_to_have_attribute("target")  # phase 26: modal, not a new tab
 
-    with page.expect_popup() as popup_info:
-        link.click()
-    viewer = popup_info.value
-    assert "back=" not in viewer.url, f"unexpected back param: {viewer.url}"
-    expect(viewer.locator("#doc-title")).to_have_text(DOC_TITLE)
+    # The exact href asserted above — no back param in the URL.
+    page.goto(f"{app_url}/document.html?source={DOC_SOURCE}&path={DOC_PATH}")
+    assert "back=" not in page.url, f"unexpected back param: {page.url}"
+    expect(page.locator("#doc-title")).to_have_text(DOC_TITLE)
     # Back link kept the default target, labeled "Sources".
-    back = viewer.locator("#doc-back")
+    back = page.locator("#doc-back")
     expect(back).to_have_attribute("href", "/sources.html")
     expect(back).to_have_text("Sources")
 
     back.click()
-    expect(viewer).to_have_url(f"{app_url}/sources.html")
-    expect(viewer.locator("#docs-table")).to_be_visible()
+    expect(page).to_have_url(f"{app_url}/sources.html")
+    expect(page.locator("#docs-table")).to_be_visible()
 
 
 # ---------------------------------------------------------------------------