feat: trigger compaction independently for the chat and compaction models - #28568

Summary

Automatic compaction now fires at whichever of two independent triggers is reached first, and the UI shows when the organization override's trigger applies.

• Chat trigger: the chat owner's personal threshold (or the chat model's) against the chat model's window. A threshold of 100 turns off only this trigger.
• Organization trigger: a fixed 80% of the organization compaction override model's window. The override model's own compression threshold is ignored. The other 20% is a target margin for the summary prompt and the summary, not a guarantee, because the trigger reads the previous step's prompt size.

On main, the chat threshold was applied to the smaller of the two windows, and nothing in the UI showed it. Example: with a 20K chat model at 70% and an 8K override, main compacts at 5,600 tokens; this PR compacts at 6,400 (80% of 8K, shown as 32%).

Changes

Backend (coderd/x/chatd):

• The trigger with the lower token point binds (ties go to the chat trigger). It drives the automatic compaction gate and the still-over-limit check, and every summary, automatic or manual, records it.
• An override that is unset, deleted, disabled, on a disabled provider, or without credentials for the chat owner is treated as absent: the chat model summarizes and only the chat trigger applies.
• The summary's output cap is bounded by the summarizer's own window, not the trigger's.
• The still-over-limit error names what can clear it: the compaction threshold (chat trigger), an override model with a larger window (organization trigger), or both when usage is over both points.
• The still-over-limit check compacts once more when the latest summary was recorded under a different threshold or trigger window. The chat_summarized result gains trigger_context_limit_tokens, and context_limit_tokens now records the chat model's window (main recorded the smaller window). On main, lowering a threshold after a compaction ended every later turn with the error.
• The still-over-limit check skips a 0% threshold ("always compact"), which on main ended the run with the error after every compaction.
• ARCHITECTURE.md documents the two triggers, the summary cap, and the still-over-limit rules.

Frontend (site), through a shared compactionTriggers helper that mirrors the backend rules (no new API):

• Coder Agents settings: the compaction override row warns when the organization trigger undercuts chat models' default triggers ("the organization override compacts chats at 80% of {model}'s {N}-token window").
• Personal thresholds page: an Effective column shows the trigger that applies, with a popover when the organization override binds. "Compacts at" follows the same trigger, and a point the chat model's window cannot reach shows as Off. The header's 100% sentence, and the row warning when a member types 100, say an organization override may still compact chats when one is set or its organization's overrides failed to load (the header also while they load).
• Chat context gauge: the compact-at percent follows the binding trigger and is annotated when the organization override binds. If the overrides request fails, it shows the chat-only value with "(organization override not loaded)", or "Compaction off (organization override not loaded)" when the chat trigger is off.
• An override whose provider the user cannot use is ignored on the gauge and the personal page, matching chatd.
• The shared formatContextLimit prints counts below 1,000 exactly (an 800-token compaction point showed "~1K") and 999,500 to 999,999 as "1.0M" instead of "1000K". It also labels the model pickers; their other values are unchanged.
• HelpPopoverIconTrigger lets callers set their own aria-label; only the Effective column's popover does.

Known v1 limits: the Coder Agents settings alert is organization-scoped, so it can warn about an override that some members fall back from for lack of provider credentials. The gauge checks the viewer's provider access, so on a shared chat its label can differ from the owner's runtime trigger (Codex P2, declined). Compaction itself is unaffected.

Screenshots

From remote UAT round 13 on 093076f: an isolated test deployment with a local fake LLM. The models are test fixtures named for their context windows: Chat model 20K (own threshold 70%), Chat model 5K (40%), and Chat model 8K (50%). Chat model 8K is also the organization compaction override, so the organization trigger is 80% of 8,000 = 6,400 tokens, which is 32% of Chat model 20K's window. Chat model 8K's own 50% applies only to chats that use it as the chat model; changing it to 10% or 100% left every value below unchanged.

Coder Agents settings: the organization trigger undercuts Chat model 20K's 70% default.

Personal thresholds: the organization trigger binds Chat model 20K at 32%. Chat model 5K (40%) and Chat model 8K (50%) keep their own chat triggers.

Personal thresholds, organization settings request failed (the first red line is the injected error). Rows fall back to chat-only values.

Chat context gauge: organization trigger binds (Chat model 20K), chat trigger binds (Chat model 5K), overrides request failed (injected).

Still-over-limit errors from real runs: organization trigger, chat trigger, both.

Testing

• Go: TestBindingCompactionTriggerSource, TestCompactionStillOverLimitError, TestCompactionStatusFromHistory, and TestActiveServer_CompactionModelOverride cover the 80% point (fails if the override's own threshold is read again), user threshold 100 leaving the organization trigger on, the summary cap for automatic and manual compaction, the over-limit messages, and recompaction after a trigger change. The site binding tests mirror the Go table row for row.
• Site: compactionTriggers unit tests and Storybook stories for the three surfaces, including the overrides fetch failure.
• On c6f8750: go vet, the chatd and chatloop tests, and the AgentsPage, AISettingsPage, and HelpPopover unit tests (2,274 passed, 2 skipped) pass, and CI is green. On 987cefe, tsc, the five affected story files (109 passed), and make pre-commit also passed. 093076f only changes ARCHITECTURE.md; the pre-commit hook's markdown format and lint checks pass on it.
• On 3cd5b08: tsc, the new formatContextLimit test (fails on the old helper for 800 and 999,999), the compactionTriggers and aiModels unit tests (224 passed), and the affected story files pass, and the pre-commit hook passed on all three commits.

Review record

• Earlier heads: 12 Codex passes and 3 human reviews, all threads answered. Rebased onto main several times, most recently ff3fa22 (kept refactor(site/src): align compaction settings table #30274, refactor(site/src/pages/AgentsPage): require always-passed settings and misc props #29892, and refactor(site/src/pages/AgentsPage): require always-passed chat input props #29890 in conflicted files).
• coder-agents-review rounds 1 to 18: findings fixed; approved since round 15. The round 1 ARCHITECTURE.md finding was left for the maintainer, who asked for the update in the last commit.
• coder-frontend-review (eight roles): all pass. Splitting the PR (RO6) was declined because it is reviewed as one unit; the organizationTriggerFor story helper stays because its three fields must match the model.
• Design change after UAT round 11: the organization trigger is a fixed 80% of the override window instead of the override model's own threshold (171d5f5, 21d2ce7, 987cefe).
• coder-agents-review round 19: copy, naming, and an unreachable zero-window gate fixed (6e8efb9, c6f8750). A summary-time fit check with chat-model fallback (CRF-156) was declined: the previous-step lag applies to every trigger, including main's. Round 20 approved c6f8750 with no findings.
• Codex: one P2 on 987cefe declined (see known limits); no major issues on c6f8750.
• Remote UAT on dogfood (fake LLM, isolated test deployment): rounds 8 to 13 PASS. Round 12 on c6f8750 first failed one criterion that was written wrong (the admin alert correctly lists an override model that is also a chat model at 100%); the reviewer endorsed PASS on the same evidence after the correction. Round 13 on 093076f retook the screenshots with neutral model names and confirmed that the override model's own threshold (10%, 50%, 100%) does not move the organization trigger.
• UAT round 13 notes: the header after a failed or pending overrides load and the sub-1K labels are fixed in 4e172ab and d5888ce; coder-agents-review round 21 found the same gap in the row warning (CRF-167, fixed in 3cd5b08). Left as on main: a summary's usage_percent is measured against the binding trigger's window, so it can exceed 100 (nothing reads it), and the 100% help text shows only for an unsaved edit.
• Codex: no major issues on d5888ce and 3cd5b08. coder-agents-review round 22 approved 3cd5b08 with no open findings.
• coder-frontend-review on those commits: all roles pass after the fixes. Declined: moving the formatter fix to its own PR (RO5; the owner asked for it here), adding "tokens" to sub-1K labels (TN6; "~800" reads like "~16K"), and splitting the component (RP6).