[chore] Remove deprecated add_rows feature

[lukasmasuch]

Describe your changes

Removes the deprecated add_rows method and all related code from the codebase.

• Removes add_rows method from ArrowMixin (previously available on st.dataframe, st.table, and chart elements)
• Removes arrowAddRows delta type from proto definitions (field 7 now reserved)
• Removes AddRowsMetadata and related helper functions from built_in_chart_utils.py
• Removes frontend handling in AppRoot.ts, ElementNode.ts, and Quiver.ts
• Deletes arrowConcatUtils.ts (Arrow concatenation utilities only used for add_rows)
• Removes all related unit tests and E2E tests
• Updates internal documentation

Breaking change: Users who relied on add_rows() will need to update their code. The method was deprecated with a warning pointing to #13063.

GitHub Issue Link (if applicable)

• Closes chart.remove_rows #299
• Closes Update width of dataframe cells upon add_rows #5860
• Closes add_rows() silently fails on compound altair chart #7994
• Closes [Request for feedback] Use-cases for add_rows #13063

Testing Plan

• Unit Tests (JS and/or Python)

Removed test files:

• lib/tests/streamlit/elements/arrow_add_rows_test.py
• e2e_playwright/st_add_rows.py and st_add_rows_test.py
• frontend/lib/src/dataframes/__snapshots__/Quiver.test.ts.snap
• Removed add_rows test sections from Quiver.test.ts, ElementNode.test.ts, vega_charts_test.py, forward_msg_queue_test.py

Agent metrics

Type	Name	Count
skill	checking-changes	1
skill	updating-internal-docs	1
subagent	fixing-pr	1
subagent	general-purpose	2
subagent	reviewing-local-changes	1
subagent	simplifying-local-changes	1

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[github-actions]

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[greptile-apps]

Greptile Summary

This PR removes the deprecated add_rows feature from the codebase, cleaning up Python backend, TypeScript frontend, proto definitions, and all related tests across 35 files. The removal is consistent and complete: proto field 7 is properly reserved, generate_chart now returns a single chart instead of a tuple, Quiver fields become readonly without mutation needed, and all callers are updated accordingly.

Confidence Score: 5/5

Safe to merge — clean, complete removal of a deprecated feature with no leftover references or broken contracts.

The removal is thorough and consistent across proto, Python backend, TypeScript frontend, and all test layers. Proto field 7 is properly reserved, generate_chart return type is correctly simplified, Quiver fields are upgraded to readonly, and all call sites are updated. No P0/P1 issues found.

No files require special attention.

Important Files Changed

Filename	Overview
proto/streamlit/proto/Delta.proto	Field 7 (arrow_add_rows) removed from Delta.oneof type and correctly added to the reserved list alongside field 5, preventing future field-number reuse.
lib/streamlit/elements/arrow.py	Removes add_rows method, _arrow_add_rows, and _prep_data_for_add_rows from ArrowMixin; cleans up related imports. Return-value docstrings updated to no longer reference .add_rows().
lib/streamlit/elements/lib/built_in_chart_utils.py	Removes AddRowsMetadata, PrepDataColumns, prep_chart_data_for_add_rows, _last_index_for_melted_dataframes, _get_pandas_index_attr. generate_chart return type simplified from tuple to single chart; horizontal and use_container_width params removed (were only used to populate AddRowsMetadata).
lib/streamlit/elements/vega_charts.py	All call sites of generate_chart updated to unpack a single chart value; add_rows_metadata parameter removed from _vega_lite_chart and all public chart methods; horizontal is now only used to choose ChartType, not forwarded to generate_chart.
frontend/lib/src/dataframes/Quiver.ts	Removes addRows(), produce/immer usage, and concat import from arrowConcatUtils. Internal data fields promoted to readonly since mutation is no longer required.
frontend/lib/src/render-tree/AppRoot.ts	Removes the arrowAddRows delta handler (including its error-to-element-node fallback) and the private arrowAddRows() tree-mutation method.
frontend/lib/src/render-tree/ElementNode.ts	Removes arrowAddRows(), quiverAddRowsHelper(), vegaLiteChartAddRowsHelper(), and getNamedDataSet() helper; produce and ArrowNamedDataSet imports cleaned up.
lib/streamlit/runtime/forward_msg_queue.py	_is_composable_message updated to only exclude new_transient delta type; add_rows/arrow_add_rows exclusions removed since those types no longer exist.
lib/streamlit/delta_generator.py	add_rows_metadata parameter removed from _enqueue and both get_locked_cursor call sites; related type annotation cleaned up.
frontend/lib/src/dataframes/arrowConcatUtils.ts	Entire file deleted — Arrow concatenation utilities were only consumed by Quiver.addRows(), which is also removed.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A["User calls st.dataframe() / st.line_chart() / etc."] --> B["DeltaGenerator._enqueue()"]
    B --> C["Cursor.get_locked_cursor(delta_type=...)"]
    C --> D["ForwardMsg with new_element delta"]
    D --> E["Frontend: AppRoot.applyDelta()"]
    E --> F{Delta type?}
    F -->|new_element| G["ElementNode created/updated"]
    F -->|new_block| H["BlockNode created/updated"]
    F -->|new_transient| I["Skipped in element tree"]
    F -->|arrowAddRows REMOVED| J["No longer exists"]
    G --> K["Quiver parses ArrowData (immutable, readonly fields)"]
    K --> L["Frontend renders chart/dataframe"]

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_{Reviews (1): Last reviewed commit: "Remove deprecated add_rows feature" | Re-trigger Greptile}

[Copilot]

Pull request overview

This PR removes the deprecated add_rows feature end-to-end (Python API surface, proto delta, frontend render-tree handling, Arrow/Quiver concat utilities, and all associated unit/E2E tests), along with a few related doc/comment updates.

Changes:

• Removes the Python add_rows API and backend helpers/metadata previously used for incremental Arrow updates.
• Removes frontend support for the arrowAddRows delta path and deletes now-unused Arrow concat utilities and test fixtures.
• Cleans up protocol usage and tests by removing arrow_add_rows usage across Python/TS/E2E suites.

Reviewed changes

Copilot reviewed 35 out of 74 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
proto/streamlit/proto/Delta.proto	Removes the arrow_add_rows delta field and reserves the field number.
lib/tests/streamlit/runtime/forward_msg_queue_test.py	Removes enqueue/flush coverage for arrow_add_rows deltas and updates expected counts.
lib/tests/streamlit/elements/vega_charts_test.py	Removes add_rows-specific chart tests.
lib/tests/streamlit/elements/arrow_add_rows_test.py	Deletes the dedicated add_rows backend unit test file.
lib/tests/streamlit/delta_generator_test.py	Updates expected DeltaGenerator public API list (drops add_rows).
lib/streamlit/testing/v1/element_tree.py	Updates element tree parsing comments now that add_rows deltas are gone.
lib/streamlit/runtime/metrics_util.py	Updates internal comment/example that referenced add_rows.
lib/streamlit/runtime/forward_msg_queue.py	Simplifies composability rules now that arrow_add_rows deltas are removed.
lib/streamlit/elements/vega_charts.py	Removes add_rows plumbing/metadata passing and updates docstrings mentioning .add_rows().
lib/streamlit/elements/lib/built_in_chart_utils.py	Removes AddRowsMetadata and add_rows-related helpers; generate_chart returns only the chart.
lib/streamlit/elements/arrow.py	Removes add_rows method and backend enqueue logic for arrow_add_rows.
lib/streamlit/delta_generator.py	Removes add_rows_metadata cursor plumbing from _enqueue and _block.
frontend/lib/src/render-tree/ElementNode.ts	Removes arrowAddRows handling for ElementNode and related dataset helper.
frontend/lib/src/render-tree/ElementNode.test.ts	Removes tests that covered ElementNode.arrowAddRows.
frontend/lib/src/render-tree/AppRoot.ts	Removes arrowAddRows delta handling and error wrapping for that path.
frontend/lib/src/mocks/arrow/fewerColumns.ts	Deletes Arrow mock data used only by add-rows concat tests.
frontend/lib/src/mocks/arrow/differentColumnTypes.ts	Deletes Arrow mock data used only by add-rows concat tests.
frontend/lib/src/dataframes/Quiver.ts	Removes Quiver.addRows and concat utility usage; makes internal fields immutable.
frontend/lib/src/dataframes/Quiver.test.ts	Removes the addRows test suite and related fixtures/imports.
frontend/lib/src/dataframes/arrowConcatUtils.ts	Deletes concat utilities that existed solely to support add_rows.
frontend/lib/src/dataframes/snapshots/Quiver.test.ts.snap	Deletes snapshots that asserted add_rows concat error messages.
frontend/lib/src/components/widgets/DataFrame/hooks/useTableSizer.ts	Updates comment that referenced row changes via add_rows.
frontend/lib/src/components/elements/ArrowVegaLiteChart/useVegaEmbed.ts	Simplifies dataset replacement log message after data changes.
frontend/lib/src/components/elements/ArrowVegaLiteChart/arrowUtils.ts	Removes incremental extraction parameter from getDataArray.
e2e_playwright/st_scatter_chart.py	Removes add-rows styling scenario from the scatter chart app script.
e2e_playwright/st_scatter_chart_test.py	Updates expected chart count and removes add-rows styling test.
e2e_playwright/st_line_chart.py	Removes add-rows styling scenario from the line chart app script.
e2e_playwright/st_line_chart_test.py	Updates expected chart count and removes add-rows styling/fullscreen test.
e2e_playwright/st_bar_chart.py	Removes add-rows styling scenario from the bar chart app script.
e2e_playwright/st_bar_chart_test.py	Updates expected chart count and removes add-rows styling test.
e2e_playwright/st_area_chart.py	Removes add-rows styling scenario from the area chart app script.
e2e_playwright/st_area_chart_test.py	Updates expected chart count and removes add-rows styling test.
e2e_playwright/st_add_rows.py	Deletes the dedicated add_rows E2E app script.
e2e_playwright/st_add_rows_test.py	Deletes the dedicated add_rows E2E test suite.
.claude/skills/understanding-streamlit-architecture/references/frontend.md	Removes internal documentation mention of arrowAddRows.

[github-actions]

📈 Frontend coverage change detected

The frontend unit test (vitest) coverage has increased by 0.0800%

• Current PR: 89.7300% (14776 lines, 1517 missed)
• Latest develop: 89.6500% (14889 lines, 1540 missed)

🎉 Great job on improving test coverage!

📊 View detailed coverage comparison

[github-actions]

Summary

This PR removes the long-deprecated add_rows API along with the entire supporting stack: the ArrowMixin.add_rows method, the arrow_add_rows proto field (now reserved 7), the AddRowsMetadata/prep_chart_data_for_add_rows chart utilities, the frontend arrowAddRows delta handler in AppRoot/ElementNode, the Quiver.addRows method along with arrowConcatUtils.ts, and all related unit/E2E tests, mock fixtures, and Quiver snapshots. Documentation references in dataframe/altair_chart/vega_lite_chart docstrings, the frontend.md architecture skill, and the metrics_util comment are updated, and the _is_composable_message exclusion set is simplified to {"new_transient"} accordingly.

Code Quality

The refactor is well-scoped, internally consistent, and idiomatic. A repo-wide search for add_rows/addRows/arrow_add_rows/arrowAddRows/AddRowsMetadata returns no remaining references. Notable cleanups that came along correctly:

• Quiver instance fields that were previously mutated only inside addRows are tightened to private readonly.
• getDataArray(quiverData, startIndex = 0) is correctly simplified to a single arg — the only previously non-zero use was on the removed add_rows path; current callers always passed 0.
• useVegaEmbed.updateData keeps its branching structure (empty new data → remove; empty prev → insert; hash diff → replace) and only drops the now-misleading "more rows" comment. Behavior is preserved.
• The ChartType.horizontal flag is no longer threaded through built_in_chart_utils.generate_chart; user-facing horizontal-bar behavior is preserved because bar_chart still selects ChartType.HORIZONTAL_BAR vs VERTICAL_BAR.
• With add_rows_metadata gone, Cursor.props / get_locked_cursor(**props) are now only exercised by their own unit tests. Not blocking, but a follow-up cleanup opportunity.

There was one inline disagreement among reviewers worth resolving here: the deletion of arrow_add_rows = 7 from Delta.proto is correct. The field number is properly retired via reserved 5, 7;, which is the standard protobuf pattern (already used for the prior 5 slot) and prevents any accidental reuse of slot 7 in future schema changes. proto3 also silently ignores unknown fields, so an older client receiving a newer message without slot 7 — or vice versa — does not break wire compatibility. No protocol-compatibility blocker here.

Test Coverage

Coverage is appropriately maintained for the surviving features:

• delta_generator_test.test_public_api is updated to drop add_rows, asserting it is no longer part of the DeltaGenerator public API.
• forward_msg_queue_test is updated to assert the new queue length now that new_element + new_element / add_block compositions are allowed.
• vega_charts_test drops the add_rows/styling-preservation tests (they only exercised removed code paths).
• The chart E2E scripts (st_line_chart.py, st_bar_chart.py, st_area_chart.py, st_scatter_chart.py) lose only the add_rows-specific scenarios, and their TOTAL_*_CHARTS counts/index comments are updated consistently.

No replacement coverage exists for the legacy .add_rows() failure path — calls like st.dataframe(df).add_rows(df2) will now raise a generic AttributeError instead of an actionable migration message. Optional follow-up.

Backwards Compatibility

This is an intentional, user-facing breaking change for an already-deprecated API. Calls like st.dataframe(df).add_rows(df2), st.table(...).add_rows(...), or chart .add_rows(...) updates will now raise AttributeError instead of emitting a deprecation warning. The PR description and labels (change:chore, impact:users) call this out, and tracking issue #13063 exists. The proto field number is correctly reserved to prevent future reuse, so older/newer client–server pairs cannot accidentally reinterpret the slot. Anyone with a third-party wrapper invoking the (private) _arrow_add_rows/prep_chart_data_for_add_rows/AddRowsMetadata symbols would also break, but those are internal and the deprecation has been visible for a long time.

Security & Risk

No security-sensitive code paths are touched: there are no changes to auth, cookies, websocket handshake, file uploads/serving, CSP headers, iframe/postMessage, OAuth, or sandbox boundaries. The Arrow concatenation logic that was removed dealt only with structural concat of pyarrow tables on the client; removing it reduces surface area rather than expanding it. The primary remaining risk is API compatibility for users of the deprecated .add_rows(), which is the intended product change.

External test recommendation

• Recommend external_test: No
• Triggered categories: None
• Evidence:
  • proto/streamlit/proto/Delta.proto: only retires a oneof slot via reserved; no transport/handshake change.
  • lib/streamlit/runtime/forward_msg_queue.py: composition exclusion list change is queue-internal, no impact on websocket framing/auth.
  • lib/streamlit/elements/arrow.py, vega_charts.py, built_in_chart_utils.py, delta_generator.py: pure API/feature removal; no routing, asset serving, embedding, storage, or SiS code touched.
  • Frontend changes (AppRoot.ts, ElementNode.ts, Quiver.ts, arrowUtils.ts, useVegaEmbed.ts) are render-tree/data-shape only; no postMessage, iframe, CSP, fetch/CORS, or service-worker behavior changed.
• Suggested external_test focus areas: None.
• Confidence: High
• Assumptions and gaps: Assumes downstream embeds/SiS deployments do not depend on receiving Delta.arrow_add_rows from a server with this change (only relevant for mismatched older client/server pairs; standard release pairing avoids this).

Accessibility

No accessibility-relevant frontend changes — the diffs are limited to data-handling logic and removal of dead code paths. No DOM/ARIA/keyboard behavior is altered.

Recommendations

1. (Merge-blocker) Delete the now-orphaned E2E snapshot images. The snapshot-hygiene.yml workflow runs on PRs that touch e2e_playwright/** and will fail because 39 PNGs are still tracked under git for tests/scenarios this PR removes:

   • The entire directory e2e_playwright/__snapshots__/linux/st_add_rows_test/ (24 files for st_dataframe-added_rows and st_vega_lite_chart-added_rows-{0..6} × {chromium, firefox, webkit}).
   • 15 chart-specific snapshots: st_line_chart_test/st_line_chart-add_rows_after_fullscreen[*].png, st_line_chart_test/st_line_chart-add_rows_preserves_styling[*].png, st_bar_chart_test/st_bar_chart-add_rows_preserves_styling[*].png, st_area_chart_test/st_area_chart-add_rows_preserves_styling[*].png, st_scatter_chart_test/st_scatter_chart-add_rows_preserves_styling[*].png.

   Run uv run python scripts/snapshot_cleanup.py locally to remove them.

2. (Optional) Consider a focused regression test (or a clearer error path) that calls .add_rows() on a dataframe/chart and confirms the new failure mode, so upgrades surface a more actionable message than a generic AttributeError.

3. (Optional) With add_rows_metadata gone, Cursor.props / get_locked_cursor(**props) are no longer consumed by production code. Consider a follow-up to drop the now-vestigial **props plumbing (and matching tests).

4. (Optional) The lazyQuiverElement/lazyVegaLiteChartElement getters in frontend/lib/src/render-tree/ElementNode.ts can no longer be reassigned by an external mutator after this PR. They still need to stay mutable for first-access lazy hydration, but the surrounding // TODO (lukasmasuch): Delete element from proto object? could be revisited now that incremental-rows mutation is gone.

Verdict

CHANGES REQUESTED: Removal is clean, well-tested, and the breaking change is intentional, but the orphaned E2E snapshot images need to be deleted before merge to avoid snapshot-hygiene CI failures.

---

This is an automated AI review consolidated by claude-opus-4-7-thinking-xhigh. Please verify the feedback and use your judgment.

This review also includes 1 inline comment(s) on specific code lines.

[github-actions]

Summary

This PR removes the deprecated add_rows() method and all related code paths end-to-end: Python public API (ArrowMixin.add_rows), backend plumbing (_arrow_add_rows, _prep_data_for_add_rows, AddRowsMetadata, prep_chart_data_for_add_rows, _get_pandas_index_attr, _last_index_for_melted_dataframes, the add_rows_metadata thread through DeltaGenerator._enqueue/_block), the Delta.arrow_add_rows protobuf field (field 7, now added to reserved), the unused ArrowNamedDataSet import, frontend render-tree handling (Quiver.addRows, arrowConcatUtils.ts, ElementNode.arrowAddRows/getNamedDataSet, the arrowAddRows branch in AppRoot.applyDelta, the [immerable] marker on Quiver, the unused startIndex param in getDataArray), the runtime composability check in forward_msg_queue._is_composable_message, all add_rows-specific Python/frontend/e2e tests, fixtures, mocks (differentColumnTypes.ts, fewerColumns.ts), snapshots, and a stale bullet from the architecture skill. Chart count constants in chart e2e tests are decremented accordingly. add_rows had been emitting a deprecation warning pointing to issue #13063, so this is a planned breaking change carrying the change:breaking / impact:users labels. As a side cleanup, generate_chart now returns alt.Chart | alt.LayerChart rather than a 2-tuple (removing awkward unpacking at every caller in vega_charts.py).

Code Quality

The deletion is unusually thorough — all reviewers independently verified that no residual references to add_rows, arrow_add_rows, arrowAddRows, or AddRowsMetadata remain in the repo (including snapshots, mocks, docs, and skill references). Imports are consistently cleaned up (ArrowNamedDataSet, ensureError, makeElementWithErrorText in AppRoot.ts; produce/immerable/concat in Quiver.ts; Hashable, npt, DataFrame, ForwardMsg, enqueue_message in arrow.py; AddRowsMetadata in vega_charts.py/delta_generator.py; cloneDeep/mock fixtures in Quiver.test.ts).

The plumbing simplifications are nice quality-of-life wins: generate_chart's tuple-to-single-value refactor, DeltaGenerator._enqueue no longer threading add_rows_metadata, and arrowUtils.getDataArray losing its unused startIndex parameter. Quiver's internal fields (_pandasIndexColumnTypes, _dataColumnTypes, _columnTypes, _pandasIndexData, _data) are correctly tightened to readonly now that mutation is gone.

A couple of small stylistic follow-ups were noted inline (a clarifying comment in _is_composable_message, an explicit elif type == "new_transient" in element_tree.py instead of a catch-all else: continue, a JSDoc note on Quiver immutability, and a follow-up to drop the now-dead **props escape hatch on Cursor.get_locked_cursor/LockedCursor). None are merge-blocking.

Test Coverage

Test removals are appropriate and targeted at the removed surface: lib/tests/streamlit/elements/arrow_add_rows_test.py (entire file), the test_add_rows* / test_*_preserves_initial_* cases in vega_charts_test.py, the ADD_ROWS_MSG fixture in forward_msg_queue_test.py (queue-length expectations correctly updated 7 → 5, 4 → 3), the ~1000-line Add rows describe-block and ~250-line ElementNode.arrowAddRows describe-block on the frontend, and e2e_playwright/st_add_rows.py / st_add_rows_test.py plus test_add_rows_preserves_styling / test_add_rows_after_fullscreen and their snapshots. Coverage for the surviving "shape" of charts (empty data, styling, stack/horizontal/sort) is preserved through the existing parametrized BuiltInChartTest cases and chart-specific test_*_styling paths.

One observation worth noting (not a regression for this PR): with ADD_ROWS_MSG gone, _is_composable_message no longer has a test that explicitly exercises a non-composable delta — new_transient is the only remaining non-composable type and isn't directly covered. Adding a small targeted test would be a nice follow-up if more delta types are introduced later.

Backwards Compatibility

This is intentionally a breaking change (PR is labeled change:breaking / impact:users):

• Apps still calling dg.add_rows(...) will raise AttributeError: 'DeltaGenerator' object has no attribute 'add_rows' after upgrade. The previous deprecation pathway (runtime warning pointing to issue #13063) prepared users for this; the release notes / changelog should explicitly call out the removal so users still on add_rows get an actionable upgrade note.
• Field 7 of Delta is correctly added to reserved, so the wire format is forward-compatible at the protobuf level — old clients that still recognize arrow_add_rows simply won't see it; the default branch in AppRoot.applyDelta will throw Unrecognized deltaType if a stale server were to send it, which is acceptable for mismatched client/server pairings.
• Reviewers disagreed on whether deleting field 7 from a "released" Delta message conflicts with proto/streamlit/proto/AGENTS.md (which restricts modifying/removing fields to unreleased messages). Established precedent (PR #13760 removed NamedDataSet add_rows = 5 from this same Delta message and used reserved 5;) supports the current approach, and the field is properly reserved here, so wire compatibility is preserved either way. Flagged inline for the author's call.
• Removing arrowConcatUtils.ts, differentColumnTypes.ts, fewerColumns.ts from frontend/lib/src/mocks/arrow/ is fine — these are internal test mocks, not part of the published @streamlit/lib API surface.
• Quiver lost its [immerable] = true marker; this is benign because addRows was the sole consumer of produce(quiver, ...) and there are no remaining call sites in the repo.

Security & Risk

No security-sensitive surfaces are touched. The diff does not modify auth, cookies, CSRF/XSRF, file upload/serving, asset routing, CSP, iframe postMessage, OAuth, secrets, or eval/Function() paths. The runtime change in forward_msg_queue.py is a pure simplification of the composable-message check and does not affect message delivery semantics for any delta type that still exists. The [immerable] removal on Quiver and the protobuf field reservation (reserved 5, 7;) are both safe in isolation.

External test recommendation

• Recommend external_test: No
• Triggered categories: None
• Key evidence:
  • proto/streamlit/proto/Delta.proto: field 7 is reserved; no transport, embedding, or routing changes.
  • lib/streamlit/runtime/forward_msg_queue.py: only the composability denylist is simplified; no handshake/session/CSRF changes.
  • No changes under lib/streamlit/web/, no changes to CSP/headers, no changes to iframed/embed code paths, no changes to upload/download endpoints, no running_in_sis() or Snowflake-runtime touches, no cookie/storage changes.
• Suggested external test focus areas: N/A (pure deletion of a deprecated public-API surface and its internal plumbing).
• Confidence: High
• Assumptions/gaps: existing chart e2e tests still re-validate end-to-end rendering of st.line_chart, st.area_chart, st.bar_chart, st.scatter_chart, and st.vega_lite_chart; their snapshots remain.

Accessibility

No accessibility-relevant frontend surfaces are touched. The removed code was non-UI rendering logic (delta application + Arrow concatenation). DOM, ARIA, focus management, and keyboard handling are unaffected.

Recommendations

1. Make sure release notes / changelog explicitly highlight the breaking removal of .add_rows() so users still on the deprecated API get an actionable upgrade note in addition to the previous deprecation warning.
2. (optional, follow-up) Consider tightening Cursor.get_locked_cursor(self, **props: Any) and the matching LockedCursor.__init__(..., **props: Any) to drop **props now that add_rows_metadata was the only consumer.
3. (optional) Consider adding a single test for _is_composable_message covering the remaining new_transient branch so the only surviving non-composable case has explicit coverage.
4. (optional) If proto/streamlit/proto/AGENTS.md is meant to strictly forbid removing fields from released messages, either switch field 7 to [deprecated=true] (and keep the field defined) or update AGENTS.md to document reserved-based removal as the accepted pattern. See inline comment.

Verdict

APPROVED: A clean, comprehensive removal of a deprecated feature with consistent backend, frontend, protobuf, and test cleanup. Two of three reviewers approved unconditionally; the third raised a protobuf-policy concern about deleting field 7 from a released Delta message, which on review is contradicted by established maintainer precedent on this same message (PR #13760), with field 7 correctly reserved to preserve wire compatibility. Remaining notes are non-blocking and tracked inline.

---

This is an automated AI review consolidated by claude-opus-4-7-thinking-xhigh from reviews by claude-opus-4-7-thinking-xhigh, gemini-3.1-pro, and gpt-5.4-xhigh. Please verify the feedback and use your judgment.

This review also includes 5 inline comment(s) on specific code lines.

[sfc-gh-lwilby-1]

LGTM